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Dziurdzik, Samantha Katarzyna

University of British Columbia

Specialized proteins facilitate inter-organelle lipid transfer at membrane contact sites (MCSs), regions where organelles are tethered in close proximity. The VPS13 proteins constitute a unique class of lipid transporters that simultaneously bridge organelles at MCSs and channel phospholipids between them. Of importance, mutations in each of the four human VPS13 (VPS13A-D) genes are associated with distinct neurological disorders, and it is thought that loss of lipid transport at specific MCSs underlies the cause of these diverse diseases. Understanding how VPS13 proteins target membranes and how their MCS recruitment is regulated is therefore crucial for developing a better understanding of the underlying disease pathologies. Here, we uncover a conserved VPS13 membrane targeting mechanism using the Saccharomyces cerevisiae model that has a single Vps13 which localizes to multiple organelles and contact sites. We identify a shared motif in the three known organelle-specific adaptors that recruit Vps13, and establish the necessity of these motifs for interaction. We find all adaptors interact at an uncharacterized six-repeat domain that we named the Vps13 Adaptor Binding (VAB) domain. We demonstrate VAB domain repeats 5–6 are sufficient for adaptor interaction and recruitment supporting a model where adaptors compete for binding to a single pocket. Importantly, modeling a spastic ataxia VPS13D missense mutation in this pocket blocks adaptor interactions, Vps13 recruitment, and further results in a vacuolar protein secretion defect that is not associated with any of the known adaptors. These findings support a conserved adaptor binding role for the VAB domain and suggest the presence of as-yet unidentified adaptors in both yeast and humans. Our studies further identify Fmp27/Hob1 and Ypr117w/Hob2 as putative Vps13 structural homologs localized at endoplasmic reticulum (ER)-plasma membrane (PM) contacts. Recruitment of ER-anchored Fmp27 to PM contacts similarly relies on interactions with a previously uncharacterized protein. Importantly, loss of this PM interactor or of both putative paralogous lipid transporters results in a redistribution of accessible sterols supporting a shared role in lipid homeostasis. Collectively, these findings support the classification of Fmp27 and Hob2 as Vps13-like lipid transporters and suggest adaptor-mediated recruitment is a common membrane targeting strategy for this class of proteins.

Text

2024-09-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85489

Medical Genetics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/