title: Get3 is a holdase chaperone and moves to deposition sites for aggregated proteins when membrane targeting is blocked.
abstract: The endomembrane system of yeast contains different tail-anchored proteins that are post-translationally targeted to membranes via their C-terminal transmembrane domain. This hydrophobic segment could be hazardous in the cytosol if membrane insertion fails, resulting in the need for energy-dependent chaperoning and the degradation of aggregated tail-anchored proteins. A cascade of GET proteins cooperates in a conserved pathway to accept newly synthesized tail-anchored proteins from ribosomes and guide them to a receptor at the endoplasmic reticulum, where membrane integration takes place. It is, however, unclear how the GET system reacts to conditions of energy depletion that might prevent membrane insertion and hence lead to the accumulation of hydrophobic proteins in the cytosol. Here we show that the ATPase Get3, which accommodates the hydrophobic tail anchor of clients, has a dual function: promoting tail-anchored protein insertion when glucose is abundant and serving as an ATP-independent holdase chaperone during energy depletion. Like the generic chaperones Hsp42, Ssa2, Sis1 and Hsp104, we found that Get3 moves reversibly to deposition sites for protein aggregates, hence supporting the sequestration of tail-anchored proteins under conditions that prevent tail-anchored protein insertion. Our findings support a ubiquitous role for the cytosolic GET complex as a triaging platform involved in cellular proteostasis.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester, M13 9PT, UK.
authors.forename: Katie
authors.initials: K
authors.lastname: Powis
authors.forename: Bianca
authors.initials: B
authors.lastname: Schrul
authors.forename: Heather
authors.initials: H
authors.lastname: Tienson
authors.forename: Irina
authors.initials: I
authors.lastname: Gostimskaya
authors.forename: Michal
authors.initials: M
authors.lastname: Breker
authors.forename: Stephen
authors.initials: S
authors.lastname: High
authors.forename: Maya
authors.initials: M
authors.lastname: Schuldiner
authors.forename: Ursula
authors.initials: U
authors.lastname: Jakob
authors.forename: Blanche
authors.initials: B
authors.lastname: Schwappach
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000378:metabolism*; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins; D000251:Adenosine Triphosphatases; C529048:Get3 protein, S cerevisiae