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Title: Probing the membrane-binding and effector function of Phage Shock Protein A and its homologue Vipp1
Author: McDonald, Christopher
ISNI:       0000 0004 5367 5431
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Stress response systems are prevalent throughout all organisms with several functioning to maintain the cell envelope. One widely distributed system in bacteria is the Phage Shock Protein (Psp) response which is involved in pathogenicity, biofilm and persister cell formation. Induced under conditions proposed to cause membrane (often Inner-Membrane, IM) stress, the Psp response appears to stabilize the IM and so prevent dissipation of the proton motive force. The central component, PspA, is a peripheral IM protein that acts as both the effector and negative regulator of the Psp response. PspA has a counterpart Vipp1, which functions for chloroplast envelope maintenance and thylakoid biogenesis in plants, algae and photosynthetic bacteria. Mechanistic insight into how PspA and Vipp1 undertake their respective effector functions is limited but thought to be through their direct interactions with cellular membranes. Rigorously controlled, in vitro methodologies with lipid vesicles, purified proteins and peptides were established and used in this study, providing the first biochemical and biophysical characterisation of membrane binding by PspA and Vipp1. Direct membrane association of PspA and Vipp1 was shown to occur through their conserved N-terminal amphipathic helices. Both proteins are found to sense stored curvature elastic (SCE) stress and anionic lipids within the membrane. PspA has enhanced sensitivity for SCE stress while Vipp1 partitioning is most sensitive to membranes with a high net-negative charge. Experimental data points to alleviation of SCE stress by Amphiphatic Helix (AH) insertions as an attractive mechanism for membrane maintenance by PspA and Vipp1. Furthermore, by probing PspA's regulatory role we show that its transcription inhibition, though binding to the transcription activator PspF, can be relieved upon bilayer exposure in a SCE stress specific manner. The identification of a physical, stress related membrane signal suggests a unilateral mechanism that promotes both membrane binding of PspA and a stress triggered induction of the Psp response.
Supervisor: Buck, Martin ; Ces, Oscar ; Zhang, Xiaodong Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral