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Subcellular Localization of Monoglucosyldiacylglycerol Synthase in Synechocystis sp PCC6803 and Its Unique Regulation by Lipid Environment
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: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 2, e88153- p.Article in journal (Refereed) Published
Abstract [en]

Synthesis of monogalactosyldiacylglycerol (GalDAG) and digalactosyldiacylglycerol (GalGalDAG), the major membrane lipids in cyanobacteria, begins with production of the intermediate precursor monoglucosyldiacylglycerol (GlcDAG), by monoglucosyldiacylglycerol synthase (MGS). In Synechocystis sp. PCC6803 (Synechocystis) this activity is catalyzed by an integral membrane protein, Sll1377 or MgdA. In silico sequence analysis revealed that cyanobacterial homologues of MgdA are highly conserved and comprise a distinct group of lipid glycosyltransferases. Global regulation of lipid synthesis in Synechocystis and, more specifically, the influence of the lipid environment on MgdA activity have not yet been fully elucidated. Therefore, we purified membrane subfractions from this organism and assayed MGS activity in vitro, with and without different lipids and other potential effectors. Sulfoquinovosyldiacylglycerol (SQDAG) potently stimulates MgdA activity, in contrast to other enzymes of a similar nature, which are activated by phosphatidylglycerol instead. Moreover, the final products of galactolipid synthesis, GalDAG and GalGalDAG, inhibited this activity. Western blotting revealed the presence of MgdA both in plasma and thylakoid membranes, with a high specific level of the MgdA protein in the plasma membrane but highest MGS activity in the thylakoid membrane. This discrepancy in the subcellular localization of enzyme activity and protein may indicate the presence of either an unknown regulator and/or an as yet unidentified MGS-type enzyme. Furthermore, the stimulation of MgdA activity by SQDAG observed here provides a new insight into regulation of the biogenesis of both sulfolipids and galactolipids in cyanobacteria.

Place, publisher, year, edition, pages
2014. Vol. 9, no 2, e88153- p.
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-101739DOI: 10.1371/journal.pone.0088153ISI: 000330830700049OAI: oai:DiVA.org:su-101739DiVA: diva2:705714
Funder
Swedish Foundation for Strategic Research
Note

AuthorCount:5;

Funding agencies:

NTU (Singapore) M4080306;

Available from: 2014-03-17 Created: 2014-03-14 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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