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Heterologous overexpression of a monotopic glucosyltransferase (MGS) induces fatty acid remodeling in Escherichia coli membranes:  
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2014 (English)In: Biochimica et Biophysica Acta - Biomembranes, ISSN 0005-2736, E-ISSN 1879-2642, Vol. 1838, no 7, 1862-1870 p.Article in journal (Refereed) Published
Abstract [en]

The membrane protein monoglucosyldiacylglycerol synthase (MGS) from Acholeplasma laidlawii is responsible for the creation of intracellular membranes when overexpressed in Escherichia coli (E. coli). The present study investigates time dependent changes in composition and properties of E. coli membranes during 22 h of MGS induction. The lipid/protein ratio increased by 38% in MGS-expressing cells compared to control cells. Time-dependent screening of lipids during this period indicated differences in fatty acid modeling. (1) Unsaturation levels remained constant for MGS cells (~ 62%) but significantly decreased in control cells (from 61% to 36%). (2) Cyclopropanated fatty acid content was lower in MGS producing cells while control cells had an increased cyclopropanation activity. Among all lipids, phosphatidylethanolamine (PE) was detected to be the most affected species in terms of cyclopropanation. Higher levels of unsaturation, lowered cyclopropanation levels and decreased transcription of the gene for cyclopropane fatty acid synthase (CFA) all indicate the tendency of the MGS protein to force E. coli membranes to alter its usual fatty acid composition.

Place, publisher, year, edition, pages
2014. Vol. 1838, no 7, 1862-1870 p.
Keyword [en]
Lipid–protein interactions, fatty acid modeling, cyclopropanation, membrane fluidity, monotopic membrane proteins, intracellular membranes
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-102674DOI: 10.1016/j.bbamem.2014.04.001ISI: 000336695300020OAI: oai:DiVA.org:su-102674DiVA: diva2:712356
Funder
Swedish Foundation for Strategic Research Swedish Research Council, 621-2006-4818Knut and Alice Wallenberg FoundationCarl Tryggers foundation Swedish Research Council, 2008-19122-62107-3Swedish Research Council, 621-2011-3524
Available from: 2014-04-14 Created: 2014-04-14 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Exploring the Interplay of Lipids and Membrane Proteins
Open this publication in new window or tab >>Exploring the Interplay of Lipids and Membrane Proteins
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interplay between lipids and membrane proteins is known to affect membrane protein topology and thus have significant effect (control) on their functions. In this PhD thesis, the influence of lipids on the membrane protein function was studied using three different membrane protein models.

A monotopic membrane protein, monoglucosyldiacylglyecerol synthase (MGS) from Acholeplasma laidlawii is known to induce intracellular vesicles when expressed in Escherichia coli. The mechanism leading to this unusual phenomenon was investigated by various biochemical and biophysical techniques. The results indicated a doubling of lipid synthesis in the cell, which was triggered by the selective binding of MGS to anionic lipids. Multivariate data analysis revealed a good correlation with MGS production. Furthermore, preferential anionic lipid sequestering by MGS was shown to induce a different fatty acid modeling of E. coli membranes. The roles of specific lipid binding and the probable mechanism leading to intracellular vesicle formation were also investigated.

As a second model, a MGS homolog from Synechocystis sp. PCC6803 was selected. MgdA is an integral membrane protein with multiple transmembrane helices and a unique membrane topology. The influence of different type of lipids on MgdA activity was tested with different membrane fractions of Synechocystis. Results indicated a very distinct profile compared to Acholeplasma laidlawii MGS. SQDG, an anionic lipid was found to be the species of the membrane that increased the MgdA activity 7-fold whereas two other lipids (PG and PE) had only minor effects on MgdA. Additionally, a working model of MgdA for the biosynthesis and flow of sugar lipids between Synechocystis membranes was proposed.

The last model system was another integral membrane protein with a distinct structure but also a different function. The envelope stress sensor, CpxA and its interaction with E. coli membranes were studied. CpxA autophosphorylation activity was found to be positively regulated by phosphatidylethanolamine and negatively by anionic lipids. In contrast, phosphorylation of CpxR by CpxA revealed to be increased with PG but inhibited by CL. Non-bilayer lipids had a negative impact on CpxA phosphotransfer activity.

Taken together, these studies provide a better understanding of the significance of the interplay of lipids and model membrane proteins discussed here.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2014. 69 p.
Keyword
Membrane lipids, membrane proteins, anionic lipids, membrane remodeling, intracellular vesicles, model membrane systems, glycosyltransferase, Escherichia coli, lipid composition, fatty acid modification, membrane curvature, bacterial homeoviscous adaptation
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-102675 (URN)978-91-7447-882-2 (ISBN)
Public defence
2014-05-16, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Available from: 2014-04-24 Created: 2014-04-14 Last updated: 2015-03-31Bibliographically approved

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