Swa2, the yeast homolog of mammalian auxilin, is specifically required for the propagation of the prion variant [URE3‐1]

Abstract

SummaryYeast prions require a core set of chaperone proteins including Sis1, Hsp70 and Hsp104 to generate new amyloid templates for stable propagation, yet emerging studies indicate that propagation of some prions requires additional chaperone activities, demonstrating chaperone specificity beyond the common amyloid requirements. To comprehensively assess such prion‐specific requirements for the propagation of the [URE 3] prion variant [URE 3‐1], we screened 12 yeast cytosolic J‐proteins, and here we report a novel role for the J‐protein Swa2/Aux1. Swa2 is the sole yeast homolog of the mammalian protein auxilin, which, like Swa2, functions in vesicle‐mediated endocytosis by disassembling the structural lattice formed by the protein clathrin. We found that, in addition to Sis1, [URE 3‐1] is specifically dependent upon Swa2, but not on any of the 11 other J‐proteins. Further, we show that [URE 3‐1] propagation requires both a functional J‐domain and the tetratricopeptide repeat (TPR) domain, but surprisingly does not require Swa2‐clathrin binding. Because the J‐domain of Swa2 can be replaced with the J‐domains of other proteins, our data strongly suggest that prion‐chaperone specificity arises from the Swa2 TPR domain and supports a model where Swa2 acts through Hsp70, most likely to provide additional access points for Hsp104 to promote prion template generation.

A Putative Biochemical Engram of Long-Term Memory

“…Hsp40, a family of chaperones (~23 in yeast and ~ 43 in Drosophila ) stimulate the ATPase activity of Hsp70 and deliver specific client proteins to Hsp70 [47]. Recent studies found different yeast prions utilizes specific Hsp40 family members [48, 49], suggesting JJJ2 may target a limited number of proteins and may modify Orb2 aggregation.…”

Prion-specific Hsp40 function: The role of the auxilin homolog Swa2

“…However, the specific portions of Sis1 required for the propagation of these prions differ, indicating that the exact roles and requirements of chaperone proteins are not universal in yeast prion propagation 6 , 26-30 . In further support of this idea, one of us (JKH) previously determined that an additional J-protein, Ydj1, is required for the propagation of [ SWI + ] specifically, 17 and we recently reported the finding that [ URE3 ] specifically requires the action of a third J-protein, Swa2 1 . Swa2 is the homolog of the mammalian protein auxilin, which is responsible for uncoating clathrin-coated vesicles during clathrin-mediated endocytosis 31 , 32 .…”

“…Others have also recently reported additional co-chaperone requirements for the propagation of [ URE3 ] 20 . Here we will review our most recent findings regarding Swa2 and prion propagation, 1 present additional data, and discuss these new results in the context of a recently published complementary investigation from another laboratory 20 . Collectively, these investigations suggest that Hsp90 may be the critical binding partner of Swa2 in [ URE3 ] propagation, and we propose a new model for plausible Swa2-Hsp90 cooperation in [ URE3 ] prion propagation.…”

“…Molecular chaperone proteins including Hsp70, the Hsp40/J-protein Sis1, and Hsp104 are required for continued prion propagation, however the specific requirements of chaperone proteins differ for various prions. We recently reported that Swa2, the yeast homolog of the mammalian protein auxilin, is specifically required for the propagation of the prion [ URE3 ] 1 . [ URE3 ] propagation requires both a functional J-domain and the tetratricopeptide repeat (TPR) domain of Swa2, but does not require Swa2 clathrin binding.…”

Hsp104 disaggregase at normal levels cures many [PSI+] prion variants in a process promoted by Sti1p, Hsp90, and Sis1p

“…Hsp70s, the cytoplasmic Ssas of Saccharomyces cerevisiae, are necessary for stable prion propagation (33)(34)(35)(36)(37), and can antagonize the curing of [PSI + ] by overproduction of Hsp104 (38), an effect requiring Sgt2 (39). The Hsp40 role in prion propagation includes considerable prion-specificity of the various Hsp40s (40,41). The need for collaboration between Hsp104, Hsp70s, Hsp40s, and nucleotide-exchange factors in prion propagation was shown by the ability of Escherichia coli homologs, ClpB, DnaK, and GrpE, to substitute for their yeast relatives only if they could interact with their E. coli partners (42).…”