An investigation into lipid exchange in the maintenance of lipid asymmetry pathway

Wotherspoon, Peter J. ORCID: 0000-0002-4973-2830 (2023). An investigation into lipid exchange in the maintenance of lipid asymmetry pathway. University of Birmingham. Ph.D.

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Abstract

The Maintenance of Lipid Asymmetry (Mla) pathway is a 6 component system implicated in the transport of phospholipids between the Gram-negative bacterial membranes, specifically in the transport of ectopic phospholipids from the outer leaflet of the outer membrane to the inner membrane. However, papers from 2019 proposed a potential role in phospholipid export. As phospholipid export to the outer membrane currently represents the last unexplored frontier of outer membrane biogenesis, the prospect of identifying a pathway responsible presents an attractive topic for further investigation. Moreover, deficiencies in Mla activity have been shown to reduce virulence and increase susceptibility to membrane destabilising agents, cementing Mla as a topic of significant interest to the field of antimicrobial research.

As such, the original objective of this project was to investigate lipid transport between the inner membrane component of the Mla pathway and the periplasmic chaperone with the intent of understanding the discrepancies between the findings in the 2019 papers and the original categorisation of Mla function. However, subsequent publications have provided clear evidence that Mla plays no role in lipid export.

Thus we chose to shift the main objective of the project to understanding the mechanism by which ATPase activity in MlaFE results in lipid exchange between MlaC and MlaD. We present structural data of a stalled intermediate complex of MlaC and MlaD, showing the binding interface, from which we have identified several residues with significant effects on lipid exchange between the two proteins. Based on these results, and existing understanding of MlaFEDB conformational changes we propose a mechanism by which ATPase induced conformational changes in MlaD might result in the expulsion of lipid from the MlaC binding pocket.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):