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

Abstract

Yeast prions are protein-based genetic elements that propagate through cell populations via cytosolic transfer from mother to daughter cell. 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. We concluded that the TPR domain determines the specificity of the genetic interaction between Swa2 and [URE3], and that this domain likely interacts with one or more proteins with a C-terminal EEVD motif. Here we extend that analysis to incorporate additional data that supports this hypothesis. We also present new data eliminating Hsp104 as the relevant Swa2 binding partner and discuss our findings in the context of other recent work involving Hsp90. Based on these findings, we propose a new model for Swa2's involvement in [URE3] propagation in which Swa2 and Hsp90 mediate the formation of a multi-protein complex that increases the number of sites available for Hsp104 disaggregation.

Variant‐specific and reciprocal Hsp40 functions in Hsp104‐mediated prion elimination

“…We hypothesized that perhaps J‐proteins other than Sis1 may be required for Hsp104‐mediated curing of weak [ PSI + ] variants. For example, we recently proposed that the J‐protein Swa2 may cooperate with Cpr7 in the propagation of [ URE3 ], and Cpr7 has been shown to be important for the curing of strong [ PSI + ] variants, which lead us to hypothesize that Swa2 could also be involved in this process (Kumar et al ., ; Oliver et al ., ). However, in order to address this and other possible roles for J‐proteins in Hsp104 curing, we first had to determine whether any cytosolic J‐protein other than Sis1 is essential for weak [ PSI + ] propagation.…”

“…[ URE3 ] is cured by overexpression of Ydj1 due to competition with Sis1 (Higurashi et al ., ; Sharma et al ., ; Reidy et al ., ) but is largely insensitive to curing by Hsp104 overexpression (Kryndushkin et al ., ; Barbitoff et al ., ; Matveenko et al ., ). The auxilin homolog Swa2 is also essential for [ URE3 ] propagation (Troisi et al ., ; Oliver et al ., ), but its role in fragmentation specifically is speculative and independent from its strict reliance on Sis1 activity (Higurashi et al ., ; Reidy et al ., ). Thus, because [ URE3 ] is relatively insensitive to Hsp104‐mediated curing, reductions in Sis1 activity provide no significant benefit but rather simply cause loss of [ URE3 ] by affecting fragmentation (Matveenko et al ., ).…”

Three J-proteins impact Hsp104-mediated variant-specific prion elimination: a new critical role for a low-complexity domain

“…Prior to our investigation, four cytosolic J-proteins were implicated in prion biology: Sis1, Apj1, Swa2, and Ydj1 (Kryndushkin et al 2002;Bradley et al 2002;Lian et al 2007;Hines et al 2011a;Hines and Craig 2011;Troisi et al 2015;Verma et al 2017;Oliver et al 2017;Killian and Hines 2018). Given 13 J-proteins at least partially inhabit the yeast cytosol (Sahi and Craig 2007) and three (Sis1, Ydj1, and Swa2) have been found to play critical roles in prion propagation, we hypothesized that other J-proteins may be involved in Hsp104-mediated curing of [PSI + ].…”

“…In addition to Sis1, three other J-proteins-Ydj1, Swa2, and Apj1-have been previously implicated in prion biology. Ydj1 is the most abundant J-protein in the yeast cytosol and is required in addition to Sis1 for propagation of the prion [SWI + ] (Ghaemmaghami et al 2003;Hines et al 2011b), whereas Swa2 is required in addition to Sis1 for the propagation of the prion [URE3] (Troisi et al 2015;Oliver et al 2017). Apj1, a J-protein similar in structure to Ydj1, is involved in the degradation of sumoylated proteins and has been demonstrated to eliminate synthetic prions when overexpressed (hence its name, "antiprion DnaJ") (Kryndushkin et al 2002;Sahi et al 2013).…”

Chaperone functional specificity promotes yeast prion diversity

“…Contrastingly, a construct of Sis1 consisting of only the J domain and GF region (Sis1-J-GF) is sufficient to maintain cell viability and to propagate some variants of [ RNQ + ] and strong but not weak variants of [ PSI + ] [ 21 , 22 , 44 ], demonstrating the existence of mutually exclusive Sis1 requirements with regard to weak [ PSI + ] and [ RNQ + ]. Finally, either alteration of Sis1 results in the loss of [ URE3 ], but deletion of the J protein Swa2 results in loss of [ URE3 ] alone [ 26 , 33 , 34 ], demonstrating that novel secondary J-protein requirements exist for some prions. Likewise, but omitted for clarity, the prion [ SWI + ] also exhibits a specific requirement for the J protein Ydj1, whereas all three other prions shown in the figure continue to propagate in a strain lacking Ydj1 [ 7 , 24 , 29 , 33 ].…”