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The Escherichia coli envelope stress sensor CpxA can sense changes in lipid bilayer properties
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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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Membrane proteins are evolutionarily integrated with their lipid bilayer environment, but it is only marginally understood how they sense and adapt to changes in lipid composition. Here we use an in vitro reconstitution system to demonstrate that the activity of envelope stress sensor CpxA of Escherichia coli is modulated by lipid bilayer properties. By changing the lipid composition of the vesicles, and using lipid-engineered E. coli strains we show that CpxA activity is regulated by means of different properties of the bilayer: (i) anionic surface charge (ii) membrane curvature (iii) thus lateral bilayer stress but also (iv) membrane bilayer thickness. We conclude that the CpxA could sense changes in the lipid bilayer properties.

Keyword [en]
CpxA envelope stress sensor, lipid bilayer stress, lipid-engineered E. coli strains, surface charge, lateral stress, membrane curvature, bilayer thickness
National Category
Natural Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-102676OAI: oai:DiVA.org:su-102676DiVA: diva2:712364
Funder
Swedish Research Council
Available from: 2014-04-14 Created: 2014-04-14 Last updated: 2014-04-15
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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