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Stress response in the cyanobacterium Synechocystis sp. PCC 6803
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Christiane Funk)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Adaptation to environmental changes is important for the survival of living organisms. Under extreme abiotic conditions, organic molecules (such as lipids, proteins and nucleic acids) are prone to damage. Under these conditions stress response mechanisms are activated, either to prevent the source of damage or to promote the rapid turnover of damaged molecules. Like all photoautotrophic organisms, cyanobacteria are sensitive to high light intensity and oxidative stress, which induces damage to the photosynthetic apparatus. My thesis is divided in two subjects related to particular stress responses in the cyanobacterium Synechocystis sp. PCC 6803: 1) the role of Deg/HtrA proteases and 2) investigations on the small CAB-like proteins.

Deg/HtrA proteases are ATP-independent serine endopeptidases with a characteristic C-terminal PDZ domain. These proteases are largely dispersed among living organisms, with many different functions, mostly involved in protein quality control. The genome of Synechocystis sp. PCC 6803 contains three genes coding for Deg/HtrA proteases: HtrA, HhoA and HhoB. These proteases are essential for survival under high light and heat stress, and may overlap in their functions. During my Ph.D. studies I focused on the identification of the precise localization of the Deg/HtrA proteases in the cyanobacterial cell, analyzed the biochemical properties of recombinant Synechocystis Deg/HtrA proteases in vitro and adopted proteomic and metabolomic approaches to study the physiological importance of these proteases. My data show that Deg/HtrA proteases are not only important in stress response mechanisms under adverse conditions, but are also involved in the stabilization of important physiological processes, such as polysaccharides biosynthesis and peptidoglycan turnover.

The small CAB-like proteins (SCPs) belong to the light harvesting-like family of stress induced proteins and are thought to be involved in the photoprotection of the photosynthetic apparatus. Five small CAB-like proteins where identified in Synechocystis sp. PCC 6803 (ScpA-E). In my studies I identified another relative to the SCPs, LilA, which I found to be co-transcribed with ScpD. I also focused on the subcellular localization and identification of potential interaction partners of the SCPs.

Place, publisher, year, edition, pages
Umeå: Department of Chemistry, Umeå University , 2011. , 49 p.
Keyword [en]
Cyanobacteria, High light, heat stress, ROS, Photosynthesis, Photosystem II, Deg/HtrA proteases, small CAB-like proteins, Refraction-2D™, MALDI-TOF, 2D-gel, GC-MS, PCA, OPLS-DA, EPS, S-layer
National Category
Biochemistry and Molecular Biology
Research subject
URN: urn:nbn:se:umu:diva-43086ISBN: 978-91-7459-201-6OAI: diva2:411426
Public defence
2011-05-13, KBC-huset, KB3B1, Umeå University, Umeå, Sweden, 13:00 (English)
Available from: 2011-04-20 Created: 2011-04-18 Last updated: 2011-04-19Bibliographically approved
List of papers
1. Association of small CAB-like proteins (SCPs) of Synechocystis sp. PCC 6803 with Photosystem II
Open this publication in new window or tab >>Association of small CAB-like proteins (SCPs) of Synechocystis sp. PCC 6803 with Photosystem II
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2008 (English)In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 95, no 2/3, 135-145 p.Article in journal (Refereed) Published
Abstract [en]

The cyanobacterial small CAB-like proteins (SCPs) are one-helix proteins with compelling similarity to the first and third transmembrane helix of proteins belonging to the CAB family of light-harvesting complex proteins in plants. The SCP proteins are transiently expressed at high light intensity and other stress conditions but their exact function remains largely unknown. Recently we showed association of ScpD with light-stressed, monomeric Photosystem II in Synechocystis sp. PCC 6803 (Yao et al. J Biol Chem 282:267-276, 2007). Here we show that ScpB associates with Photosystem II at normal growth conditions. Moreover, upon introduction of a construct into Synechocystis so that ScpB is expressed continuously under normal growth conditions, ScpE was detected under non-stressed conditions as well, and was copurified with tagged ScpB and Photosystem II. We also report on a one-helix protein, Slr1544, that is somewhat similar to the SCPs and whose gene is cotranscribed with that of ScpD; Slr1544 is another member of the extended light-harvesting-like (Lil) protein family, and we propose to name it LilA.

Place, publisher, year, edition, pages
SpringerLink, 2008
Antenna, Chlorophyll-binding protein, Cyanobacteria, Early-light induced proteins (ELIPs), High-light induced proteins (HLIPs), Light-harvesting complex, Synechocystis sp. PCC 6803
urn:nbn:se:umu:diva-16688 (URN)10.1007/s11120-007-9244-3 (DOI)17912610 (PubMedID)
Available from: 2008-05-30 Created: 2008-05-30 Last updated: 2011-04-19Bibliographically approved
2. Recombinant Deg/HtrA proteases from Synechocystis sp. PCC 6803 differ in substrate specificity, biochemical characteristics and mechanism
Open this publication in new window or tab >>Recombinant Deg/HtrA proteases from Synechocystis sp. PCC 6803 differ in substrate specificity, biochemical characteristics and mechanism
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2011 (English)In: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 435, no 3, 733-742 p.Article in journal (Refereed) Published
Abstract [en]

Cyanobacteria require efficient protein quality control mechanisms to survive under dynamic, often stressful environmental conditions. It was reported that three serine proteases, HtrA, HhoA and HhoB are important for survival of Synechocystis sp. PCC 6803 under high light and temperature stresses and might have redundant physiological functions. Here we show that all three proteases can degrade unfolded model substrates, but differ in respect to cleavage sites, temperature and pH optima. For recombinant HhoA, and to a lesser extent for HtrA, we observed an interesting shift in the pH optimum from slightly acidic to alkaline in the presence of Mg2+ and Ca2+ ions. All three proteases formed different homo-oligomeric complexes with and without substrate, implying mechanistic differences in comparison to each other and to the well-studied Escherichia coli orthologues DegP and DegS. Deletion of the PDZ domain decreased, but not abolished proteolytic activity of all three proteases, and prevented substrate-induced formation of complexes higher than trimers by HtrA and HhoA. In summary, biochemical characterisation of HtrA, HhoA and HhoB lays the foundation for a better understanding of their overlapping, but not completely redundant stress resistance functions in Synechocystis sp. PCC 6803.

urn:nbn:se:umu:diva-40402 (URN)10.1042/BJ20102131 (DOI)21332448 (PubMedID)
Published as BJ Immediate Publication 21 February 2011 Available from: 2011-03-10 Created: 2011-02-22 Last updated: 2015-02-16Bibliographically approved

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