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Membrane Stored Curvature Elastic Stress Modulates Recruitment of Maintenance Proteins PspA and Vipp1.

McDonald C, Jovanovic G, Ces O, Buck M - MBio (2015)

Bottom Line: Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane.Our work points to alleviation of membrane stored curvature elastic stress by amphipathic helix insertions as an attractive mechanism for membrane maintenance by PspA and Vipp1.Furthermore, the identification of a physical, stress-related membrane signal suggests a unilateral mechanism that promotes both binding of PspA and induction of the Psp response.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Imperial College London, London, United Kingdom Institute of Chemical Biology, Imperial College London, London, United Kingdom.

No MeSH data available.


Related in: MedlinePlus

Membrane binding of PspA as a function of lipid composition. (a) Binding of PspA to vesicles (100 nm) composed of E. coli lipids extracted from WT, cls (deficient in CL), and pgsA (deficient in PG and CL) at increasing lipid concentrations. (b) Membrane binding of PspA to zwitterionic vesicles compositions of increasing SCE stress (from DMPC/DOPC 4:6 to DOPE/DOPC 4:6) at 0.5 and 1.5 mM lipid concentrations. (c) PspA binding as a function of SCE stress within vesicles at increasing lipid concentrations. Differences in binding between vesicle compositions were statistically significant at all lipid concentrations (P  < 0.05). (d) Binding of PspA to DMPC/DOPC 4:6 (low-SCE stress) vesicles containing different percentages of the anionic lipids PG (DOPG), CL (14:0 CL), and PS (DOPS). All experiments (in this and remaining figures unless otherwise stated) were carried out in triplicate with different vesicle preparations, and error bars represent standard errors. (e) Binding of PspA as a function of anionic lipid content and SCE stress. Binding levels to vesicles with low (DMPC/DOPC 4:6) and high (DOPE/DOPC 4:6) SCE stress with and without 10% anionic DOPG are shown.
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fig2: Membrane binding of PspA as a function of lipid composition. (a) Binding of PspA to vesicles (100 nm) composed of E. coli lipids extracted from WT, cls (deficient in CL), and pgsA (deficient in PG and CL) at increasing lipid concentrations. (b) Membrane binding of PspA to zwitterionic vesicles compositions of increasing SCE stress (from DMPC/DOPC 4:6 to DOPE/DOPC 4:6) at 0.5 and 1.5 mM lipid concentrations. (c) PspA binding as a function of SCE stress within vesicles at increasing lipid concentrations. Differences in binding between vesicle compositions were statistically significant at all lipid concentrations (P  < 0.05). (d) Binding of PspA to DMPC/DOPC 4:6 (low-SCE stress) vesicles containing different percentages of the anionic lipids PG (DOPG), CL (14:0 CL), and PS (DOPS). All experiments (in this and remaining figures unless otherwise stated) were carried out in triplicate with different vesicle preparations, and error bars represent standard errors. (e) Binding of PspA as a function of anionic lipid content and SCE stress. Binding levels to vesicles with low (DMPC/DOPC 4:6) and high (DOPE/DOPC 4:6) SCE stress with and without 10% anionic DOPG are shown.

Mentions: To probe the contributions of native E. coli phospholipids to PspA-membrane binding, vesicles produced from cell extracts were used. Zwitterionic PE, anionic phosphatidylglycerol (PG), and dianionic CL make up around 75%, 20%, and 5% of the IM phospholipid content of E. coli, respectively (21). Strains of E. coli lacking the CL synthase gene (cls) have greatly diminished amounts of CL, while strains lacking the PG synthase gene (pgsA) have significantly reduced PG and CL (22). Lipids were extracted from E. coli WT cells and from cls and pgsA deletion mutants. Mass spectrometry of the extracts confirmed a great reduction in PG for the pgsA mutant (data not shown). PspA bound vesicles of the three lipid extracts with a similar affinity (Fig. 2a), as the slight differences in binding between the extracts were statistically insignificant at any of the lipid concentrations tested (for all comparisons, P > 0.05, repeated-measures analysis of variance [ANOVA]). Our results imply that membranes deficient in anionic lipids can still bind PspA. Although low levels of anionic lipids within the pgsA vesicles and <1% phosphatidylserine (PS) are present in membranes (23), our results suggest that a high anionic lipid content in membranes is not a requirement for PspA binding.


Membrane Stored Curvature Elastic Stress Modulates Recruitment of Maintenance Proteins PspA and Vipp1.

McDonald C, Jovanovic G, Ces O, Buck M - MBio (2015)

Membrane binding of PspA as a function of lipid composition. (a) Binding of PspA to vesicles (100 nm) composed of E. coli lipids extracted from WT, cls (deficient in CL), and pgsA (deficient in PG and CL) at increasing lipid concentrations. (b) Membrane binding of PspA to zwitterionic vesicles compositions of increasing SCE stress (from DMPC/DOPC 4:6 to DOPE/DOPC 4:6) at 0.5 and 1.5 mM lipid concentrations. (c) PspA binding as a function of SCE stress within vesicles at increasing lipid concentrations. Differences in binding between vesicle compositions were statistically significant at all lipid concentrations (P  < 0.05). (d) Binding of PspA to DMPC/DOPC 4:6 (low-SCE stress) vesicles containing different percentages of the anionic lipids PG (DOPG), CL (14:0 CL), and PS (DOPS). All experiments (in this and remaining figures unless otherwise stated) were carried out in triplicate with different vesicle preparations, and error bars represent standard errors. (e) Binding of PspA as a function of anionic lipid content and SCE stress. Binding levels to vesicles with low (DMPC/DOPC 4:6) and high (DOPE/DOPC 4:6) SCE stress with and without 10% anionic DOPG are shown.
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Related In: Results  -  Collection

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fig2: Membrane binding of PspA as a function of lipid composition. (a) Binding of PspA to vesicles (100 nm) composed of E. coli lipids extracted from WT, cls (deficient in CL), and pgsA (deficient in PG and CL) at increasing lipid concentrations. (b) Membrane binding of PspA to zwitterionic vesicles compositions of increasing SCE stress (from DMPC/DOPC 4:6 to DOPE/DOPC 4:6) at 0.5 and 1.5 mM lipid concentrations. (c) PspA binding as a function of SCE stress within vesicles at increasing lipid concentrations. Differences in binding between vesicle compositions were statistically significant at all lipid concentrations (P  < 0.05). (d) Binding of PspA to DMPC/DOPC 4:6 (low-SCE stress) vesicles containing different percentages of the anionic lipids PG (DOPG), CL (14:0 CL), and PS (DOPS). All experiments (in this and remaining figures unless otherwise stated) were carried out in triplicate with different vesicle preparations, and error bars represent standard errors. (e) Binding of PspA as a function of anionic lipid content and SCE stress. Binding levels to vesicles with low (DMPC/DOPC 4:6) and high (DOPE/DOPC 4:6) SCE stress with and without 10% anionic DOPG are shown.
Mentions: To probe the contributions of native E. coli phospholipids to PspA-membrane binding, vesicles produced from cell extracts were used. Zwitterionic PE, anionic phosphatidylglycerol (PG), and dianionic CL make up around 75%, 20%, and 5% of the IM phospholipid content of E. coli, respectively (21). Strains of E. coli lacking the CL synthase gene (cls) have greatly diminished amounts of CL, while strains lacking the PG synthase gene (pgsA) have significantly reduced PG and CL (22). Lipids were extracted from E. coli WT cells and from cls and pgsA deletion mutants. Mass spectrometry of the extracts confirmed a great reduction in PG for the pgsA mutant (data not shown). PspA bound vesicles of the three lipid extracts with a similar affinity (Fig. 2a), as the slight differences in binding between the extracts were statistically insignificant at any of the lipid concentrations tested (for all comparisons, P > 0.05, repeated-measures analysis of variance [ANOVA]). Our results imply that membranes deficient in anionic lipids can still bind PspA. Although low levels of anionic lipids within the pgsA vesicles and <1% phosphatidylserine (PS) are present in membranes (23), our results suggest that a high anionic lipid content in membranes is not a requirement for PspA binding.

Bottom Line: Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane.Our work points to alleviation of membrane stored curvature elastic stress by amphipathic helix insertions as an attractive mechanism for membrane maintenance by PspA and Vipp1.Furthermore, the identification of a physical, stress-related membrane signal suggests a unilateral mechanism that promotes both binding of PspA and induction of the Psp response.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Imperial College London, London, United Kingdom Institute of Chemical Biology, Imperial College London, London, United Kingdom.

No MeSH data available.


Related in: MedlinePlus