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  • 1.
    Ahmadova, Nigar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Tyrosine D oxidation and redox equilibrium in Photosystem II2017In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 6, p. 407-417Article in journal (Refereed)
    Abstract [en]

    Tyrosine ID (Tyr(D)) is an auxiliary redox active tyrosine residue in photosystem II (PSII). The mechanism of Tyr(D) oxidation was investigated by EPR spectroscopy, flash-induced fluorescence decay and thermoluminescence measurements in PSII enriched membranes from spinach. PSII membranes were chemically treated with 3 mM ascorbate and 1 mM diaminodurene and subsequent washing, leading to the complete reduction of Tyr(D). Tyr(D) oxidation kinetics and competing recombination reactions were measured after a single saturating flash in the absence and presence of DCMU (inhibitor of the Q(B)-site) in the pH range of 4.7-8.5. Two kinetic phases of Tyro oxidation were observed by the time resolved EPR spectroscopy the fast phase (msec-sec time range) and the pH dependent slow phase (tens of seconds time range). In the presence of DCMU, Tyr(D) oxidation kinetics was monophasic in the entire pH range, i.e. only the fast kinetics was observed. The results obtained from the fluorescence and thermoluminescence analysis show that when forward electron transport is blocked in the presence of DCMU, the S(2)Q((S) over bar) recombination outcompetes the slow phase of Tyr(D) oxidation by the S-2 state. Modelling of the whole complex of these electron transfer events associated with Tyr(D) oxidation fitted very well with our experimental data. Based on these data, structural information and theoretical considerations we confirm our assignment of the fast and slow oxidation kinetics to two populations of PSII centers with different water positions (proximal and distal) in the Tyr(D) vicinity.

  • 2. Cox, Nicholas
    et al.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Pewnim, Naray
    Steffen, Ronald
    Smith, Paul J.
    Havelius, Kajsa G. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Hughes, Joseph L.
    Debono, Lesley
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Krausz, Elmars
    Pace, Ron J.
    The S-1 split signal of photosystem II: a tyrosine-manganese coupled interaction2009In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1787, no 7, p. 882-889Article in journal (Refereed)
    Abstract [en]

    Detailed optical and EPR analyses of states induced in dark-adapted PS II membranes by cryogenic illumination permit characterization and quantification of all pigment derived donors and acceptors, as well as optically silent (in the visible, near infrared) species which are EPR active. Near complete turnover formation of Q(A)(-) is seen in all centers, but with variable efficiency, depending on the donor species. In minimally detergent-exposed PS II membranes, negligible (<5%) oxidation of chlorophyll or carotenoid centers occurs for illumination temperatures 5-20 K. An optically silent electron donor to P680(+) is observed with the same decay kinetics as the S-1 split signal. Cryogenic donors to P680(+) seen are: (i) transient (t(1/2)similar to 150 s) tyrosine related species, including 'split signals' (similar to 15% total centers), (ii) reduced cytochrome b(559) (similar to 30-50% centers), and (iii) an organic donor, possibly an amino acid side chain, (similar to 30% centers).

  • 3.
    Elmgren, Maja
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Åkesson, Eva
    Uppsala University, University Administration.
    Schmid, Siegbert
    University of Sydney, School of Chemistry.
    Towns, Marcy
    Purdue University, Department of Chemistry.
    Comparison and Evaluation of Learning Outcomes from an International Perspective: Development of a Best-Practice Process2015In: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328, Vol. 92, no 3, p. 427-432Article in journal (Refereed)
    Abstract [en]

    Chemistry education focused on learning outcomes is increasingly practiced, providing new opportunities for international comparisons. The interest in intended learning outcomes and constructive alignment has grown in many parts of the world due to both research in higher education and political decisions. In an International Union of Pure and Applied Chemistry (IUPAC) project, we have developed a method of using critical evaluation of learning outcomes and descriptors at international, national, and institutional levels to enhance learner-centered chemistry education. This method is process-focused, aimed at learning by sharing and comparing practices around the world. Three overarching documents for the chemistry bachelor from the USA, Europe and Australia were compared. The differences were found to be more in style than in content. A tool for self-analysis was constructed to evaluate how learning outcomes for courses and modules are linked to each other and to learning outcomes for educational programs and how the expected learning outcomes can be aligned with learning activities and assessment. We conclude that the method can be used to elucidate the correspondence between learning outcomes at different levels, and the constructive alignment between learning outcomes, learning activities and assessment. The process gives new perspectives and shared knowledge. Chemistry education may need to be different depending on local considerations, and awareness of these differences is of value for further development.

  • 4.
    Han, Guangye
    et al.
    Institute of Botany, The Chinese Academy of Sciences.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Havelius, Kajsa G. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Morvaridi, Susan F.
    Department of Chemistry and Biochemistry, University of California-Los Angeles,.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Direct quantification of the four individual S states in Photosystem II using EPR spectroscopy2008In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1777, no 6, p. 496-503Article in journal (Refereed)
    Abstract [en]

    Car, carotenoid; Chl, chlorophyll; ChlZ, secondary chlorophyll electron donor to P680+; Cytb559, cytochrome b559; EPR, electron paramagnetic resonance; DMSO, dimethylsulfoxide; MES, 2-(N-morpholino) ethanesulfonic acid; NIR, near-infrared; OEC, oxygen evolving complex; P680, primary electron donor chlorophylls in PSII; PpBQ, phenyl-p-benzoquinone; PSII, Photosystem II; QA and QB, primary and secondary plastoquinone acceptors of Photosystem II; YD, tyrosine 161 of the PSII D2 polypeptide; YZ, tyrosine 161 of the PSII D1 polypeptide

  • 5. Han, Guangye
    et al.
    Morvaridi, Susan
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    S-state dependence of misses in the OEC probed by EPR spectroscopy of individual S-states2008In: Photosynthesis. Energy from the Sun / [ed] Allen J.F., Gant E., Golbeck J.H. and Osmond B., Springer , 2008, p. 419-422Conference paper (Refereed)
  • 6.
    Havelius, Kajsa G. V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Sjöholm, Johannes
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Metalloradical EPR Signals from the Y-Z center dot S-State Intermediates in Photosystem II2010In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 37, no 1-4, p. 151-176Article, review/survey (Refereed)
    Abstract [en]

    The redox-active tyrosine residue (Y-Z) plays a crucial role in the mechanism of the water oxidation. Metalloradical electron paramagnetic resonance (EPR) signals reflecting the light-induced Y-Z center dot in magnetic interaction with the CaMn4-cluster in the particular S-state, Y-Z center dot S-X intermediates, have been found in intact photosystem II. These so-called split EPR signals are induced by illumination at cryogenic temperatures and provide means to both study the otherwise transient Y-Z center dot and to probe the S-states with EPR spectroscopy. The illumination used for signal induction grouped the observed split EPR signals in two categories: (i) Y-Z in the lower S-states was oxidized by P680(+) formed via charge separation, while (ii) Y-Z in the higher S-states was oxidized by an excited, highly oxidizing Mn species. Applied mechanistic studies of the Y-Z center dot S-X intermediates in the different S-states are reviewed and compared to investigations in photosystem II at physiological temperature. Addition of methanol induced S-state characteristic changes in the split signals' formation which reflect changes in the magnetic coupling within the CaMn4-cluster due to methanol binding. The pH titration of the split EPR signals, on the other hand, could probe the proton-coupled electron transfer properties of the Y-Z oxidation. The apparent pK (a)s found for decreased split signal induction were interpreted in the fate of the phenol proton.

  • 7.
    Havelius, Kajsa G. V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Su, Ji-Hu
    Han, Guangye
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    The formation of the split EPR signal from the S-3 state of Photosystem II does not involve primary charge separation2011In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1807, no 1, p. 11-21Article in journal (Refereed)
    Abstract [en]

    Metalloradical EPR signals have been found in intact Photosystem II at cryogenic temperatures. They reflect the light-driven formation of the tyrosine Z radical (Y-z(center dot)) in magnetic interaction with the CaMn4 cluster in a particular S state. These so-called split EPR signals, induced at cryogenic temperatures, provide means to study the otherwise transient Y-z(center dot) and to probe the S states with EPR spectroscopy. In the S-0 and S-1 states, the respective split signals are induced by illumination of the sample in the visible light range only. In the S-3 state the split EPR signal is induced irrespective of illumination wavelength within the entire 415-900 nm range (visible and near-IR region) [Su, J. H., Havelius, K. G. V., Ho, F. M., Han, G., Mamedov, F., and Styring, S. (2007) Biochemistry 46. 10703-10712]. An important question is whether a single mechanism can explain the induction of the Split S-3 signal across the entire wavelength range or whether wavelength-dependent mechanisms are required. In this paper we confirm that the Y-z(center dot) radical formation in the S-1 state, reflected in the Split S-1 signal, is driven by P680-centered charge separation. The situation in the S-3 state is different. In Photosystem II centers with pre-reduced quinone A (Q(A)), where the P680-centered charge separation is blocked, the Split S-3 EPR signal could still be induced in the majority of the Photosystem II centers using both visible and NIR (830 nm) light. This shows that P680-centered charge separation is not involved. The amount of oxidized electron donors and reduced electron acceptors (Q(A)(-)) was well correlated after visible light illumination at cryogenic temperatures in the S-1 state. This was not the case in the S-3 state, where the Split S-3 EPR signal was formed in the majority of the centers in a pathway other than P680-centered charge separation. Instead, we propose that one mechanism exists over the entire wavelength interval to drive the formation of the Split S-3 signal. The origin for this, probably involving excitation of one of the Mn ions in the CaMn4 cluster in Photosystem II, is discussed.

  • 8. Havelius, Kajsa
    et al.
    Su, Ji-Hu
    Ho, Felix
    Han, Guangye
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    The mechanism behind the formation of the “Split S3” EPR signal in photosystem II induced by visible or near-infrared light2008In: Photosynthesis. Energy from the Sun / [ed] Allen J.F., Gant E., Golbeck J.H. and Osmond B., Springer , 2008, p. 423-426Conference paper (Refereed)
  • 9.
    Hayes, Sarah
    et al.
    University of Limerick.
    McHugh, Martin
    University of Limerick.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    RAw Communication and Engagement2018In: Electronic Proceedings of the ESERA 2017 Conference. Research, Practice and Collaboration in Science Education., 2018Conference paper (Refereed)
  • 10.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Reforms in pedagogy and the Confucian tradition: looking below the surface2018In: Cultural Studies of Science Education, ISSN 1871-1502, E-ISSN 1871-1510, Vol. 13, no 1, p. 133-145Article in journal (Refereed)
    Abstract [en]

    This Forum article addresses some of the issues raised in the article by Ying-Syuan Huang and Anila Asghar's paper entitled: Science education reform in Confucian learning cultures: teachers' perspectives on policy and practice in Taiwan. An attempt is made to highlight the need for a more nuanced approach in considering the Confucian education tradition and its compatibility with education reforms. In particular, the article discusses issues concerning the historical development of the Confucian education tradition, challenges in reform implementation that are in reality tradition-independent, as well as opportunities and points of convergence that the Confucian education tradition presents that can in fact be favorable to implementation of reform-based pedagogies.

  • 11.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Structural and mechanistic investigations of photosystem II through computational methods2012In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1817, no 1, p. 106-120Article, review/survey (Refereed)
    Abstract [en]

    The advent of oxygenic photosynthesis through water oxidation by photosystem II (PSII) transformed the planet, ultimately allowing the evolution of aerobic respiration and an explosion of ecological diversity. The importance of this enzyme to life on Earth has ironically been paralleled by the elusiveness of a detailed understanding of its precise catalytic mechanism. Computational investigations have in recent years provided more and more insights into the structural and mechanistic details that underlie the workings of PSII. This review will present an overview of some of these studies, focusing on those that have aimed at elucidating the mechanism of water oxidation at the CaMn(4) cluster in PSII, and those exploring the features of the structure and dynamics of this enzyme that enable it to catalyse this energetically demanding reaction. This article is part of a Special Issue entitled: Photosystem II.

  • 12.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Turning Challenges into Opportunities for Promoting Systems Thinking through Chemistry EducationIn: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328Article in journal (Refereed)
    Abstract [en]

    Systems thinking encompasses a set of skills forunderstanding, analyzing, and working with systems consisting ofmultiple interconnected elements and exhibiting emergent properties.Such systems are all around us, and helping students to develop suchskills is central to equipping them to tackle professional and societalchallenges. While the implementation of systems thinking approaches ineducation is increasingly widespread in disciplines such as biology,engineering, and geosciences, it is as yet not widespread in chemistry.This article aims to identify challenges in chemistry education that couldbe turned into opportunities for introducing concepts relevant tosystems and systems thinking, so that students improve their conceptualunderstanding of chemistry at the same time as they develop theirsystems thinking skills. Suggestions and examples of possible productivepedagogical approaches are also outlined and discussed.

  • 13.
    Ho, Felix M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Elmgren, Maja
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Rodriguez, Jon-Marc G.
    Purdue University.
    Bain, Kinsey R.
    Michigan State University.
    Towns, Marcy H.
    Purdue University.
    Graphs: Working with Models at the Crossroad between Chemistry and Mathematics2019In: It’s Just Math: Research on Students’ Understanding of Chemistry and Mathematics, American Chemical Society (ACS), 2019, p. 47-67Chapter in book (Refereed)
    Abstract [en]

    The use and interpretation of graphs pose significant challenges to the learner, but also open up opportunities for developing skills in combining both chemical and mathematical knowledge in problem solving. The analysis of a task in chemical kinetics serves in this chapter as the basis for discussing the design and use of open-ended problems through the lens of a number of frameworks, with the aim of providing the practitioner with practical examples, as well as tools and insights for further investigations and ways to help improve student learning.

  • 14.
    Ho, Felix M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Morvaridi, Susan F.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Enhancement of Y-D(center dot) spin relaxation by the CaMn4 cluster in photosystem II detected at room temperature: A new probe for the S-cycle2007In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1767, no 1, p. 5-14Article in journal (Refereed)
    Abstract [en]

    The long-lived, light-induced radical Y-D(.) of the Tyr161 residue in the D2 protein of Photosystem 11 (PSII) is known to magnetically interact with the CaMn4 cluster, situated similar to 30 angstrom away. In this study we report a transient step-change increase in YD EPR intensity upon the application of a single laser flash to S, state-synchronised PSII-enriched membranes from spinach. This transient effect was observed at room temperature and high applied microwave power (100 mW) in samples containing PpBQ, as well as those containing DCMU. The subsequent decay lifetimes were found to differ depending on the additive used. We propose that this flash-induced signal increase was caused by enhanced spin relaxation of YD by the OEC in the S-2 state, as a consequence of the single laser flash turnover. The post-flash decay reflected S-2 -> S-1 back-turnover, as confirmed by their correlations with independent measurements of S-2 multiline EPR signal and flash-induced variable fluorescence decay kinetics under corresponding experimental conditions. This flash-induced effect opens up the possibility to study the kinetic behaviour of S-state transitions at room temperature using YD as a probe.

  • 15.
    Ho, Felix M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Access channels and methanol binding site to the CaMn4 cluster in Photosystem II based on solvent accessibility simulations, with implications for substrate water access2008In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1777, no 2, p. 140-153Article in journal (Refereed)
    Abstract [en]

    Given the tightly packed environment of Photosystem II (PSII), channels are expected to exist within the protein to allow the movement of small molecules to and from the oxygen evolving centre. In this report, we calculate solvent contact surfaces from the PSII crystal structures to identify such access channels for methanol and water molecules. In a previous study of the effects of methanol on the EPR split S-1-, S-3-, and S-0-signals [Su et al. (2006) Biochemistry 45, 7617-7627], we proposed that methanol binds to one and the same Mn ion in all S-states. We find here that while channels of methanol dimensions were able to make contact with the CaMn4 cluster, only Mn-3 and Mn-4 were accessible to methanol. Combining this observation with spectroscopic data in the literature, we propose that Mn-3 is the ion to which methanol binds. Furthermore, by calculating solvent contact surfaces for water, we found analogous and more extensive water accessible channels within PSII. On the basis of their structure, orientation, and electrostatic properties, we propose functional assignments of these channels as passages for substrate water access to the CaMn4 cluster, and for the exit of O-2 and H+ that are released during water oxidation. Finally, we discuss the possible existence of a gating mechanism for the control of substrate water access to the CaMn4 cluster, based on the observation of a gap within the channel system that is formed by Ca2+ and several mechanistically very significant residues in the vicinity of the cluster.

  • 16.
    Howe, Christoph
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Nenninger, Anja
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Raleiras, Patricia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Stensjö, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Differential biochemical properties of three canonical Dps proteins from the cyanobacterium Nostoc punctiforme suggest distinct cellular functions2018In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 293, no 43, p. 16635-16646Article in journal (Refereed)
    Abstract [en]

    DNA-binding proteins from starved cells (Dps, EC: 1.16.3.1) have a variety of different biochemical activities such as DNA-binding, iron sequestration, and H2O2 detoxification. Most bacteria commonly feature one or two Dps enzymes, whereas the cyanobacterium Nostoc punctiforme displays an unusually high number of five Dps proteins (NpDps1-5). Our previous studies have indicated physiological differences, as well as cell-specific expression, among these five proteins. Three of the five NpDps proteins, NpDps1, -2, and -3, were classified as canonical Dps proteins. To further investigate their properties and possible importance for physiological function, here we characterized and compared them in vitro Nondenaturing PAGE, gel filtration, and dynamic light-scattering experiments disclosed that the three NpDps proteins exist as multimeric protein species in the bacterial cell. We also demonstrate Dps-mediated iron oxidation catalysis in the presence of H2O2 However, no iron oxidation with O2 as the electron acceptor was detected under our experimental conditions. In modeled structures of NpDps1, -2, and -3, protein channels were identified that could serve as the entrance for ferrous iron into the dodecameric structures. Furthermore, we could demonstrate pH-dependent DNA-binding properties for NpDps2 and -3. This study adds critical insights into the functions and stabilities of the three canonical Dps proteins from N. punctiforme and suggests that each of the Dps proteins within this bacterium has a specific biochemical property and function.

  • 17.
    Howe, Christoph
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Moparthi, Vamsi
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Department of Physics, Chemistry and Biology, Division of Chemistry, Linköping University, Linköping, Sweden.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Persson, Karina
    Department of Chemistry, Umeå University, Umeå, Sweden.
    Stensjö, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    The Dps4 from Nostoc punctiforme ATCC 29133 is a member of His-type FOC containing Dps protein class that can be broadly found among cyanobacteria2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 8, article id e0218300Article in journal (Refereed)
    Abstract [en]

    Dps proteins (DNA-binding proteins from starved cells) have been found to detoxify H2O2. At their catalytic centers, the ferroxidase center (FOC), Dps proteins utilize Fe2+ to reduce H2O2 and therefore play an essential role in the protection against oxidative stress and maintaining iron homeostasis. Whereas most bacteria accommodate one or two Dps, there are five different Dps proteins in Nostoc punctiforme, a phototrophic and filamentous cyanobacterium. This uncommonly high number of Dps proteins implies a sophisticated machinery for maintaining complex iron homeostasis and for protection against oxidative stress. Functional analyses and structural information on cyanobacterial Dps proteins are rare, but essential for understanding the function of each of the NpDps proteins. In this study, we present the crystal structure of NpDps4 in its metal-free, iron- and zinc-bound forms. The FOC coordinates either two iron atoms or one zinc atom. Spectroscopic analyses revealed that NpDps4 could oxidize Fe2+ utilizing O2, but no evidence for its use of the oxidant H2O2 could be found. We identified Zn2+ to be an effective inhibitor of the O2-mediated Fe2+ oxidation in NpDps4. NpDps4 exhibits a FOC that is very different from canonical Dps, but structurally similar to the atypical one from DpsA of Thermosynechococcus elongatus. Sequence comparisons among Dps protein homologs to NpDps4 within the cyanobacterial phylum led us to classify a novel FOC class: the His-type FOC. The features of this special FOC have not been identified in Dps proteins from other bacterial phyla and it might be unique to cyanobacterial Dps proteins.

  • 18. Howe, Christoph
    et al.
    Moparthi, Vamsi K.
    Ho, Felix M.
    Persson, Karina
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stensjo, Karin
    The Dps4 from Nostoc punctiforme ATCC 29133 is a member of His-type FOC containing Dps protein class that can be broadly found among cyanobacteria2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 8, article id e0218300Article in journal (Refereed)
    Abstract [en]

    Dps proteins (DNA-binding proteins from starved cells) have been found to detoxify H2O2. At their catalytic centers, the ferroxidase center (FOC), Dps proteins utilize Fe2+ to reduce H2O2 and therefore play an essential role in the protection against oxidative stress and maintaining iron homeostasis. Whereas most bacteria accommodate one or two Dps, there are five different Dps proteins in Nostoc punctiforme, a phototrophic and filamentous cyanobacterium. This uncommonly high number of Dps proteins implies a sophisticated machinery for maintaining complex iron homeostasis and for protection against oxidative stress. Functional analyses and structural information on cyanobacterial Dps proteins are rare, but essential for understanding the function of each of the NpDps proteins. In this study, we present the crystal structure of NpDps4 in its metal-free, iron-and zinc-bound forms. The FOC coordinates either two iron atoms or one zinc atom. Spectroscopic analyses revealed that NpDps4 could oxidize Fe2+ utilizing O-2, but no evidence for its use of the oxidant H2O2 could be found. We identified Zn2+ to be an effective inhibitor of the O-2-mediated Fe2+ oxidation in NpDps4. NpDps4 exhibits a FOC that is very different from canonical Dps, but structurally similar to the atypical one from DpsA of Thermosynechococcus elongatus. Sequence comparisons among Dps protein homologs to NpDps4 within the cyanobacterial phylum led us to classify a novel FOC class: the His-type FOC. The features of this special FOC have not been identified in Dps proteins from other bacterial phyla and it might be unique to cyanobacterial Dps proteins.

  • 19.
    Linke, Katrin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Water in Photosystem II: Structural, functional and mechanistic considerations2014In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1837, no 1, p. 14-32Article, review/survey (Refereed)
    Abstract [en]

    Water is clearly important for the functioning of Photosystem II (PSII). Apart from being the very substrate that needs to be transported in this water oxidation enzyme, water is also vital for the transport of protons to and from the catalytic center as well as other important co-factors and key residues in the enzyme. The latest crystal structural data of PSII have enabled detailed analyses of the location and possible function of water molecules in the enzyme. Significant progress has also been made recently in the investigation of channels and pathways, through the protein complex. Through these studies, the mechanistic significance of water for PSII is becoming increasingly clear. An overview and discussion of key aspects of the current research on water in PSII is presented here. The role of water in three other systems (aquaporin, bacteriorhodopsin and cytochrome P450) is also outlined to illustrate further points concerning the central significance that water can have, and potential applications of these ideas for continued research on PSII. It is advocated that water be seen as an integral part of the protein and far from a mere solvent.

  • 20.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Krassen, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Stensjö, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Modeling Photosystem I with the alternative reaction center protein PsaB2 in the nitrogen fixing cyanobacterium Nostoc punctiforme2011In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1807, no 9, p. 1152-1161Article in journal (Refereed)
    Abstract [en]

    Five nitrogen fixing cyanobacterial strains have been found to contain PsaB2, an additional and divergent gene copy for the Photosystem I reaction center protein PsaB. In all five species the divergent gene, psaB2, is located separately from the normal psaAB operon in the genome. The protein, PsaB2, was recently identified in heterocysts of Nostoc punctiforme sp. strain PCC 73102. 12 conserved amino acid replacements and one insertion, were identified by a multiple sequence alignment of several PsaB2 and PsaB1 sequences. Several, including an inserted glutamine, are located close to the iron-sulfur cluster F(x) in the electron transfer chain. By homology modeling, using the Photosystem I crystal structure as template, we have found that the amino acid composition in PsaB2 will introduce changes in critical parts of the Photosystem I protein structure. The changes are close to F(x) and the phylloquinone (PhQ) in the B-branch, indicating that the electron transfer properties most likely will be affected. We suggest that the divergent PsaB2 protein produces an alternative Photosystem I reaction center with different structural and electron transfer properties. Some interesting physiologcial consequences that this can have for the function of Photosystem I in heterocysts, are discussed.

  • 21.
    Magnuson, Ann
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Raleiras, Patricia
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Meszaros, Livia S.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Khanna, Namita
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Miranda, Helder
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lindblad, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Sustainable photobiological hydrogen production via protein engineering of cyanobacterial hydrogenases2018In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 22.
    McHugh, Martin
    et al.
    University of Limerick.
    Hayes, Sarah
    University of Limerick.
    Stapleton, Aimee
    University of Limerick.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    RAw Communications and Engagement (RACE):: Teaching Science Communication through Modular Design2019In: Research into practice in chemistry education:  Selected contributions from the 25th IUPAC International Conference on Chemistry Education 2018, Springer Nature Singapore , 2019Chapter in book (Refereed)
    Abstract [en]

    This project is motivated by an increasing demand from public bodies and research funding agencies for outreach and public engagement, believing this to be a path towards enhanced public understanding, recruitment and research with impact. Yet many STEM (Science, Technology, Engineering and Mathematics) graduates and professionals lack the appropriate communication skills required to  engage with the public. To address some of these issues, the project RACE (RAw Communication and Engagement) was jointly initiated by universities and industrial partners across Europe. Through the design and implementation of adaptable modules incorporating content knowledge, scientific communication and public engagement skills, this international project aims to equip students and researchers alike to ground their work within the wider global society and communicate their research with public audiences. A key feature is the direct incorporation of actual public engagement activities into RACE modules, for the mutual benefit of participants and wider society. Given this, the chapter will take a practitioner perspective to shed light on the inner workings of a modular scientific communication course. Core issues of engagement, bridging theory and practice, evaluation and collaboration are all highlighted through reflections and research data from implementing the RACE programme as a PhD summer school with doctoral level students. The chapter is concluded by bringing forward core teaching and learning protocols that are integral to running the RACE programme.

  • 23.
    Miao, Rui
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Xie, Hao
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lindblad, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Protein engineering of α-ketoisovalerate decarboxylase for improved isobutanol production in Synechocystis PCC 68032018In: Metabolic engineering, ISSN 1096-7176, E-ISSN 1096-7184, Vol. 47, p. 42-48Article in journal (Refereed)
    Abstract [en]

    Protein engineering is a powerful tool to modify e.g. protein stability, activity and substrate selectivity. Heterologous expression of the enzyme α-ketoisovalerate decarboxylase (Kivd) in the unicellular cyanobacterium Synechocystis PCC 6803 results in cells producing isobutanol and 3-methyl-1-butanol, with Kivd identified as a potential bottleneck. In the present study, we used protein engineering of Kivd to improve isobutanol production in Synechocystis PCC 6803. Isobutanol is a flammable compound that can be used as a biofuel due to its high energy density and suitable physical and chemical properties. Single replacement, either Val461 to isoleucine or Ser286 to threonine, increased the Kivd activity significantly, both in vivo and in vitro resulting in increased overall production while isobutanol production was increased more than 3-methyl-1-butanol production. Moreover, among all the engineered strains examined, the strain with the combined modification V461I/S286T showed the highest (2.4 times) improvement of isobutanol-to-3M1B molar ratio, which was due to a decrease of the activity towards 3M1B production. Protein engineering of Kivd resulted in both enhanced total catalytic activity and preferential shift towards isobutanol production in Synechocystis PCC 6803.

  • 24.
    Raleiras, Patrícia
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Khanna, Namita
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Miranda, Helder
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Meszaros, Livia S.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Krassen, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Battchikova, Natalia
    Turku University.
    Aro, Eva-Mari
    Turku University.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Lindblad, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Turning around the electron flow in an uptake hydrogenase. EPR spectroscopy and in vivo activity of a designed mutant in HupSL from Nostoc punctiforme2016In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 9, no 2, p. 581-594Article in journal (Refereed)
    Abstract [en]

    The filamentous cyanobacterium Nostoc punctiforme ATCC 29133 produces hydrogen via nitrogenase in heterocysts upon onset of nitrogen-fixing conditions. N. punctiforme expresses concomitantly the uptake hydrogenase HupSL, which oxidizes hydrogen in an effort to recover some of the reducing power used up by nitrogenase. Eliminating uptake activity has been employed as a strategy for net hydrogen production in N. punctiforme (Lindberg et al., Int. J. Hydrogen Energy, 2002, 27, 1291-1296). However, nitrogenase activity wanes within a few days. In the present work, we modify the proximal iron-sulfur cluster in the hydrogenase small subunit HupS by introducing the designed mutation C12P in the fusion protein f-HupS for expression in E. coli (Raleiras et al., J. Biol. Chem., 2013, 288, 18345-18352), and in the full HupSL enzyme for expression in N. punctiforme. C12P f-HupS was investigated by EPR spectroscopy and found to form a new paramagnetic species at the proximal cluster site consistent with a [4Fe-4S] to [3Fe-4S] cluster conversion. The new cluster has the features of an unprecedented mixed-coordination [3Fe-4S] metal center. The mutation was found to produce stable protein in vitro, in silico and in vivo. When C12P HupSL was expressed in N. punctiforme, the strain had a consistently higher hydrogen production than the background [capital Delta]hupSL mutant. We conclude that the increase in hydrogen production is due to the modification of the proximal iron-sulfur cluster in HupS, leading to a turn of the electron flow in the enzyme.

  • 25.
    Rodriguez, Jon-Marc G.
    et al.
    Purdue University.
    Bain, Kinsey
    Michigan State University.
    Towns, Marcy H.
    Purdue University.
    Elmgren, Maja
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Covariational reasoning and mathematical narratives: investigating students' understanding of graphs in chemical kinetics2019In: Chemistry Education Research and Practice, ISSN 1756-1108, E-ISSN 1756-1108, Vol. 20, no 1, p. 107-119Article in journal (Refereed)
    Abstract [en]

    Graphical representations are an important tool used to model abstract processes in fields such as chemistry. Successful interpretation of a graph involves a combination of mathematical expertise and discipline-specific content to reason about the relationship between the variables and to describe the phenomena represented. In this work, we studied students’ graphical reasoning as they responded to a chemical kinetics prompt. Qualitative data was collected and analyzed for a sample of 70 students through the use of an assessment involving short-answer test items administered in a first-year, non-majors chemistry course at a Swedish university. The student responses were translated from Swedish to English and subsequently coded to analyze the chemical and mathematical ideas students attributed to the graph. Mathematical reasoning and ideas related to covariation were analyzed using graphical forms and the shape thinking perspective of graphical reasoning. Student responses were further analyzed by focusing on the extent to which they integrated chemistry and mathematics. This was accomplished by conceptualizing modeling as discussing mathematical narratives, characterizing how students described the “story” communicated by the graph. Analysis provided insight into students’ understanding of mathematical models of chemical processes.

  • 26. Rozman Grinberg, Inna
    et al.
    Berglund, Sigrid
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hasan, Mahmudul
    Lundin, Daniel
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Magnuson, Ann
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Logan, Derek T.
    Sjöberg, Britt-Marie
    Berggren, Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Class Id ribonucleotide reductase utilizes a Mn2(IV,III) cofactor and undergoes large conformational changes on metal loading2019In: Journal of Biological Inorganic Chemistry, ISSN 0949-8257, E-ISSN 1432-1327, Vol. 24, no 6, p. 863-877Article in journal (Refereed)
    Abstract [en]

    Outside of the photosynthetic machinery, high-valent manganese cofactors are rare in biology. It was proposed that a recently discovered subclass of ribonucleotide reductase (RNR), class Id, is dependent on a Mn2(IV,III) cofactor for catalysis. Class I RNRs consist of a substrate-binding component (NrdA) and a metal-containing radical-generating component (NrdB). Herein we utilize a combination of EPR spectroscopy and enzyme assays to underscore the enzymatic relevance of the Mn2(IV,III) cofactor in class Id NrdB from Facklamia ignava. Once formed, the Mn2(IV,III) cofactor confers enzyme activity that correlates well with cofactor quantity. Moreover, we present the X-ray structure of the apo- and aerobically Mn-loaded forms of the homologous class Id NrdB from Leeuwenhoekiella blandensis, revealing a dimanganese centre typical of the subclass, with a tyrosine residue maintained at distance from the metal centre and a lysine residue projected towards the metals. Structural comparison of the apo- and metal-loaded forms of the protein reveals a refolding of the loop containing the conserved lysine and an unusual shift in the orientation of helices within a monomer, leading to the opening of a channel towards the metal site. Such major conformational changes have not been observed in NrdB proteins before. Finally, in vitro reconstitution experiments reveal that the high-valent manganese cofactor is not formed spontaneously from oxygen, but can be generated from at least two different reduced oxygen species, i.e. H2O2 and superoxide (O 2 ·− ). Considering the observed differences in the efficiency of these two activating reagents, we propose that the physiologically relevant mechanism involves superoxide.

  • 27. Sicora, Cosmin Ionel
    et al.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Salminen, Tiina
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Aro, Eva-Mari
    Transcription of a "silent" cyanobacterial psbA gene is induced by microaerobic conditions2009In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1787, no 2, p. 105-112Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria, contrary to higher plants, have a small psbA gene family encoding the reaction centre D1 protein subunit of photosystem 11, the first macromolecular pigment-protein complex of the photosynthetic electron transport chain. Modulation of expression of multiple psbA genes in the family allows cyanobacteria to adapt to changing environmental conditions. To date, two different strategies for regulation of the psbA genes have emerged. One, characterized in Synechocystis; PCC6803 and Gloeobacter violaceus PCC7421 involves the increased expression of one type of D1 protein to cope with the increased rate of damage. The other strategy, in Synechococcus PCC7942 and Anabaena PCC7120, is to replace the existing D1 with a new D1 form for the duration of the stress. However, most of the psbA gene families characterized to date contain also a divergent, apparently silent psbA gene of unknown function. This gene, present in Synechocystis, Anabaena and Thermosynechococcus elongatus BP-1 was not induced by any stress condition applied so far. Our data shows a reversible induction of the divergent psbA gene during the onset of argon-induced microaerobic conditions in Synechocystis, Anabaena and Thermosynechococcus elongatus. The unitary functional response of three unrelated cyanobacterial species, namely the induction of the expression of the divergent psbA gene as a reaction to the same environmental cue, indicates that these genes and the protein they encode are part of a specific cellular response to microaerobic conditions. There are no specific primary structure similarities between the different microaerobic inducible D1 forms, designated as D1'. Only three amino acid residues are consistently conserved in D1'. These modifications are: G80 to A, F158 to L and 1286 to L In silico mutation of the published D1 structure from Thermosynechococcus did not reveal major modifications. The point by point effects of the mutations on the local environment of the PSII structure are also discussed.

  • 28.
    Sjöholm, Johannes
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Chen, Guiying
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Split Electron Paramagnetic Resonance Signal Induction in Photosystem II Suggests Two Binding Sites in the S-2 State for the Substrate Analogue Methanol2013In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 52, no 21, p. 3669-3677Article in journal (Refereed)
    Abstract [en]

    Illuminating a photosystem II sample at low temperatures (here 5-10 K) yields so-called split signals detectable with continuous wave-electron paramagnetic resonance (CW-EPR). These signals reflect the oxidized, deprotonated radical of DI-Tyr161 (Y-z(center dot)) in a magnetic interaction with the CaMn4 cluster in a particular S state. The intensity of the split EPR signals are affected by the addition of the water substrate analogue methanol. This was previously shown by the induction of split EPR signals from the S-1, S-3, and S-0 states [Su, J.-H. et al. (2006) Biochemistry 45, 7617-7627.]. Here, we use two split EPR signals induced from photosystem II trapped in the S-2 state to further probe the binding of methanol in an S state dependent manner. The signals are induced with either visible or near-infrared light illumination provided at 5-10 K where methanol cannot bind or unbind from its site. The results imply that the binding of methanol not only changes the magnetic properties of the CaMn4 cluster but also the hydrogen bond network in the oxygen evolving complex (OEC), thereby affecting the relative charge of the S2 state. The induction mechanisms for the two split EPR signals are different resulting in two different redox states, S2Yz center dot and S1Yz center dot respectively. The two states show different methanol dependence for their induction. This indicates the existence of two binding sites for methanol in the CaMn4 cluster. It is proposed that methanol binds to Mn-A with high affinity and to Mn-D with lower affinity. The molecular nature and S-state dependence of the methanol binding to each respective site are discussed.

  • 29.
    Sjöholm, Johannes
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Chen, Guiying
    Ho, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Split Electron Paramagnetic Resonance signal induction in photosystem II suggests two binding sites in the S2 state for the substrate analogue methanol2013In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 52, no 21, p. 3669-3677Article in journal (Refereed)
    Abstract [en]

    Illuminating a photosystem II sample at low temperatures (here 5–10 K) yields so-called split signals detectable with continuous wave-electron paramagnetic resonance (CW-EPR). These signals reflect the oxidized, deprotonated radical of D1-Tyr161 (YZ) in a magnetic interaction with the CaMn4 cluster in a particular S state. The intensity of the split EPR signals are affected by the addition of the water substrate analogue methanol. This was previously shown by the induction of split EPR signals from the S1, S3, and S0 states [Su, J.-H. et al. (2006) Biochemistry 45, 7617–7627.]. Here, we use two split EPR signals induced from photosystem II trapped in the S2 state to further probe the binding of methanol in an S state dependent manner. The signals are induced with either visible or near-infrared light illumination provided at 5–10 K where methanol cannot bind or unbind from its site. The results imply that the binding of methanol not only changes the magnetic properties of the CaMn4 cluster but also the hydrogen bond network in the oxygen evolving complex (OEC), thereby affecting the relative charge of the S2 state. The induction mechanisms for the two split EPR signals are different resulting in two different redox states, S2YZ and S1YZ respectively. The two states show different methanol dependence for their induction. This indicates the existence of two binding sites for methanol in the CaMn4 cluster. It is proposed that methanol binds to MnA with high affinity and to MnD with lower affinity. The molecular nature and S-state dependence of the methanol binding to each respective site are discussed.

  • 30.
    Sjöholm, Johannes
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Stockholm Univ, Dept Biochem & Biophys, Arrhenius Labs Nat Sci, SE-10691 Stockholm, Sweden..
    Ho*, Felix
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ahmadova, Nigar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Brinkert, Katharina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Imperial Coll London, Dept Life Sci, Sir Ernst Chain Bldg, London SW7 2AZ, England..
    Hammarström, Leif
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Mamedov*, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    The protonation state around Tyr(D)/Tyr((D)) over dot in photosystem II is reflected in its biphasic oxidation kinetics2017In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 2, p. 147-155Article in journal (Refereed)
    Abstract [en]

    The tyrosine residue D2-Tyr160 (Tyr(D)) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from Tyr(D) has been followed using time resolved EPR spectroscopy after triggering the oxidation of pre-reduced Tyr(D) by a short laser flash. After its oxidation Tyro is observed as a neutral radical (Tyr((D)) over dot) indicating that the oxidation is coupled to a deprotonation event. The redox state of Tyro was reported to be determined by the two water positions identified in the crystal structure of PSII [Saito et al. (2013) Proc. Natl. Acad. Sci. USA 110, 7690]. To assess the mechanism of the proton coupled electron transfer of Tyr(D) the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of Tyro oxidation at different H/D concentrations. Two kinetic phases of Tyro oxidation - the fast phase (msec-sec time range) and the slow phase (tens of seconds time range) were resolved as was previously reported [Vass and Styring (1991) Biochemistry 30, 830]. In the presence of deuterated buffers the kinetics was significantly slower compared to normal buffers. Furthermore, although the kinetics were faster at both high pH and pD values the observed KIE was found to be similar (similar to 2.4) over the whole pL range investigated. We assign the fast and slow oxidation phases to two populations of PSII centers with different water positions, proximal and distal respectively, and discuss possible deprotonation events in the vicinity of Tyro.

  • 31.
    Sjöholm, Johannes
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Havelius, Kajsa G.V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Visible light induction of an EPR split signal in photosystem II in the S2 state reveals the importance of charges in the oxygen evolving center during catalysis: a unifying model2012In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 51, no 10, p. 2054-2064Article in journal (Refereed)
    Abstract [en]

    Cryogenic illumination of Photosystem II (PSII) can lead to the trapping of the metastable radical Y-z(center dot), the radical form of the redox-active tyrosine residue D1-Tyr161 (known as Y-z). Magnetic interaction between this radical and the CaMn4 cluster of PSII gives rise to so-called split electron paramagnetic resonance (EPR) signals with characteristics that are dependent on the S state. We report here the observation and characterization of a split EPR signal that can be directly induced from PSII centers in the S-2 state through visible light illumination at 10 K. We further show that the induction of this split signal takes place via a Mn-centered mechanism, in the same way as when using near-infrared light illumination [Koulougliotis, D., et al. (2003) Biochemistry 42, 3045-3053]. On the basis of interpretations of these results, and in combination with literature data for other split signals induced under a variety of conditions (temperature and light quality), we propose a unified model for the mechanisms of split signal induction across the four S states (S-0, S-1, S-2, and S-3). At the heart of this model is the stability or instability of the Y-z(center dot)(D1-His190)(+) pair that would be formed during cryogenic oxidation of Y-Z. Furthermore, the model is closely related to the sequence of transfers of protons and electrons from the CaMn4, cluster during the S cycle and further demonstrates the utility of the split signals in probing the immediate environment of the oxygen-evolving center in PSII.

  • 32.
    Su, Ji-Hu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Havelius, Kajsa G V.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Ho, Felix M.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Han, Guangye
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Mamedov, Fikret
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Styring, Stenbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science, Molecular Biomimetics.
    Formation Spectra of the EPR Split Signals from the S(0), S(1), and S(3) States in Photosystem II Induced by Monochromatic Light at 5 K2007In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 46, no 37, p. 10703-10712Article in journal (Refereed)
    Abstract [en]

    The interaction EPR split signals from photosystem II (PSII) have been reported from the S0, S1, and S3 states. The signals are induced by illumination at cryogenic temperatures and are proposed to reflect the magnetic interaction between YZ* and the Mn4Ca cluster. We have investigated the formation spectra of these split EPR signals induced in PSII enriched membranes at 5 K using monochromatic laser light from 400 to 900 nm. We found that the formation spectra of the split S0, split S1, and split S3 EPR signals were quite similar, but not identical, between 400 and 690 nm, with maximum formation at 550 nm. The major deviations were found between 440 and 480 nm and between 580 and 680 nm. In the regions around 460 and 680 nm the amplitudes of the formation spectra were 25-50% of that at 550 nm. A similar formation spectrum was found for the S2-state multiline EPR signal induced at 0 degrees C. In general, the formation spectra of these signals in the visible region resemble the reciprocal of the absorption spectra of our PSII membranes. This reflects the high chlorophyll concentration necessary for the EPR measurements which mask the spectral properties of other absorbing species. No split signal formation was found by the application of infrared laser illumination between 730 and 900 nm from PSII in the S0 and S1 states. However, when such illumination was applied to PSII membranes poised in the S3 state, formation of the split S3 EPR signal was observed with maximum formation at 740 nm. The quantum yield was much less than in the visible region, but the application of intensive illumination at 830 nm resulted in accumulation of the signal to an amplitude comparable to that obtained with illumination with visible light. The split S3 EPR signal induced by NIR light was much more stable at 5 K (no observable decay within 60 min) than the split S3 signal induced by visible light (50% of the signal decayed within 30 min). The split S3 signals induced by each of these light regimes showed the same EPR spectral features and microwave power saturation properties, indicating that illumination of PSII in the S3 state by visible light or by NIR light produces a similar configuration of YZ* and the Mn4Ca cluster.

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