Structure and function of PspA and Vipp1 N-terminal peptides: Insights into the membrane stress sensing and mitigation

Christopher Mcdonald,Goran Jovanovic,B.A Wallace,Oscar Ces,Martin Buck

doi:10.1016/j.bbamem.2016.10.018

Christopher Mcdonald, Goran Jovanovic + Show 3 more

Open Access

https://doi.org/10.1016/j.bbamem.2016.10.018

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Abstract

The phage shock protein (Psp) response maintains integrity of the inner membrane (IM) in response to extracytoplasmic stress conditions and is widely distributed amongst enterobacteria. Its central component PspA, a member of the IM30 peripheral membrane protein family, acts as a major effector of the system through its direct association with the IM. Under non-stress conditions PspA also negatively regulates its own expression via direct interaction with the AAA+ ATPase PspF. PspA has a counterpart in cyanobacteria called Vipp1, which is implicated in protection of the thylakoid membranes. PspA's and Vipp1's conserved N-terminal regions contain a putative amphipathic helix a (AHa) required for membrane binding. An adjacent amphipathic helix b (AHb) in PspA is required for imposing negative control upon PspF. Here, purified peptides derived from the putative AH regions of PspA and Vipp1 were used to directly probe their effector and regulatory functions. We observed direct membrane-binding of AHa derived peptides and an accompanying change in secondary structure from unstructured to alpha-helical establishing them as bona fide membrane-sensing AH's. The peptide-binding specificities and their effects on membrane stability depend on membrane anionic lipid content and stored curvature elastic stress, in agreement with full length PspA and Vipp1 protein functionalities. AHb of PspA inhibited the ATPase activity of PspF demonstrating its direct regulatory role. These findings provide new insight into the membrane binding and function of PspA and Vipp1 and establish that synthetic peptides can be used to probe the structure-function of the IM30 protein family.

Highlights

The cell envelope provides protection from the environment and gives structural integrity to the cell in all organisms
The results obtained in this work establish that the N-terminal amphipathic helix (AH) of PspA and Vipp1, amphipathic helix a (AHa), is an inner membrane (IM)-binding determinant which may act as a membrane stress-sensing AH
This provides strong evidence for a direct lipid interaction between the Nterminal AHa of PspA and Vipp1 being responsible for the specific membrane binding

Summary

Introduction

The cell envelope provides protection from the environment and gives structural integrity to the cell in all organisms. Homeostasis of the plasma membrane is vital for functioning of the cell and the bacterial phage shock protein (Psp) response protects the bacterial membrane under various extracytoplasmic stress conditions. The Psp response rescues the proton gradient and conserves the pmf by protecting the plasma membrane integrity. The central component of the Psp system is the peripheral plasma membrane binding protein PspA belonging to the IM30 family of proteins found in many organisms. The Psp response and PspA-like proteins are implicated in protein translocation, virulence and resistance to antimicrobials that target the cell wall or reorganise the membrane architecture [3,5,6,7,8,9]

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