Cns1 Is an Activator of the Ssa1 ATPase Activity

Hainzl, Otmar; Wegele, Harald; Richter, Klaus; Büchner, Johannes

doi:10.1074/jbc.m402189200

Cited by 46 publications

(38 citation statements)

References 55 publications

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“…While direct biochemical evidence is lacking to confirm this hypothesis, strong indirect evidence exists in the form of biochemical analysis of equivalent DnaK mutations (Mayer et al 2001) and also the effect of Hsp40 and TPR cochaperones on ATPase stimulation of Ssa1p (Cyr et al 1992;Wegele et al 2003;Hainzl et al 2004). Promoting the interaction of Hsp70-Ssa with the prion substrate may disrupt the finely tuned ATPase hydrolysis cycle and thus prevent prion propagation by not releasing substrate for prion conversion.…”

Section: A176tmentioning

confidence: 99%

Importance of the Hsp70 ATPase Domain in Yeast Prion Propagation

2007

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The Saccharomyces cerevisiae non-Mendelian genetic element [PSI 1 ] is the prion form of the translation termination factor Sup35p. The ability of [PSI 1 ] to propagate efficiently has been shown previously to depend upon the action of protein chaperones. In this article we describe a genetic screen that identifies an array of mutants within the two major cytosolic Hsp70 chaperones of yeast, Ssa1p and Ssa2p, which impair the propagation of [PSI

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Section: A176tmentioning

confidence: 99%

Importance of the Hsp70 ATPase Domain in Yeast Prion Propagation

2007

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“…Proteins containing TPR domains with the dicarboxylate clamp in S. cerevisiae has also been shown to interact with molecular chaperones. Tom70 has been shown to interact with both Ssa1 and Hsc82 to facilitate protein import into mitochondrion (Young et al 2003 (Wegele et al 2003) and Cns1 (Hainzl et al 2004) are capable of stimulating the ATPhydrolytic activity of Ssa1. In this report, we demonstrated that a previously uncharacterized TPR-containing protein, Sgt2 (Kordes et al 1998), in S. cerevisiae has the capacity to interact with members of Ssa molecular chaperones.…”

Section: Introductionmentioning

confidence: 99%

SGT2 and MDY2 interact with molecular chaperone YDJ1 in Saccharomyces cerevisiae

2007

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In Saccharomyces cerevisiae, Sgt2 was thought to be the homologue of vertebrate SGT (small glutamine tetratricopeptide repeat-containing protein). SGT has been known to interact with both Hsp70 and Hsp90. However, it was not clear whether Sgt2 might have a similar capacity. Here, we showed that Ssa1/Ssa2 (yeast heat shock cognate [Hsc]70), Hsc82 (yeast Hsp90), and Hsp104 coprecipitated with Sgt2 from yeast lysates. Another molecular chaperone, Ydj1, known to interact with Ssa1 and Hsc82, also coprecipitated with Sgt2. Synthetic lethality between SGT2 and YDJ1 was observed after the cells were under stress, although Sgt2 might not interact physically with Ydj1. We also found that Mdy2 interacted with the N-terminal region of Sgt2 and that Mdy2 appeared to interact physically with Ydj1. Mdy2 therefore may mediate the association of Ydj1 and Sgt2. In addition, the mating efficiency of mdy2⌬, sgt2⌬, and mdy2⌬sgt2⌬ strains was reduced to a similar extent. Compared with mdy2⌬ and ydj1⌬ cells, ydj1⌬mdy2⌬ cells, however, showed a further suppression in mating efficiency. Moreover, MDY2 interacted genetically with YDJ1. These results suggest that protein complexes containing Sgt2 and Mdy2 bring molecular chaperones together to carry out certain chaperoning functions.

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“…Ssa ATPase activity, and therefore protein folding capacity, is in turn governed by modulatory proteins such as the DnaJ homolog, Ydj1, which stimulates ATPase activity up to 10-fold, and Fes1, recently identified as a nucleotide exchange factor (11,12). In addition, Sti1 and Cns1, two tetratricopeptide repeat proteins associated with the Hsp90 chaperone complex, were recently demonstrated to strongly activate Ssa1 (13,14). Another pair of Hsp70 proteins in yeast, functionally distinct from the Ssa chaperones, are encoded by SSB1 and SSB2.…”

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confidence: 99%

The Yeast Hsp110 Sse1 Functionally Interacts with the Hsp70 Chaperones Ssa and Ssb

Shaner¹,

Wegele

Büchner

et al. 2005

Journal of Biological Chemistry

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120

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There is growing evidence that members of the extended Hsp70 family of molecular chaperones, including the Hsp110 and Grp170 subgroups, collaborate in vivo to carry out essential cellular processes. However, relatively little is known regarding the interactions and cellular functions of Sse1, the yeast Hsp110 homolog. Through co-immunoprecipitation analysis, we found that Sse1 forms heterodimeric complexes with the abundant cytosolic Hsp70s Ssa and Ssb in vivo. Furthermore, these complexes can be efficiently reconstituted in vitro using purified proteins. Binding of Ssa or Ssb to Sse1 was mutually exclusive. The ATPase domain of Sse1 was found to be critical for interaction as inactivating point mutations severely reduced interaction with Ssa and Ssb. Sse1 stimulated Ssa1 ATPase activity synergistically with the co-chaperone Ydj1, and stimulation required complex formation. Ssa1 is required for post-translational translocation of the yeast mating pheromone ␣-factor into the endoplasmic reticulum. Like ssa mutants, we demonstrate that sse1⌬ cells accumulate prepro-␣-factor, but not the co-translationally imported protein Kar2, indicating that interaction between Sse1 and Ssa is functionally significant in vivo. These data suggest that the Hsp110 chaperone operates in concert with Hsp70 in yeast and that this collaboration is required for cellular Hsp70 functions.Cells respond to protein-denaturing stresses such as heat by rapidly inducing expression of a wide array of heat shock genes. Chief among these are the molecular chaperones, highly conserved proteins that associate with and protect unfolded proteins, preventing their aggregation and supporting refolding (1). Perhaps the most abundant and well characterized chaperones are the heat shock protein 70 (Hsp70) 2 family, found in all cell types from bacteria to eukaryotes (2, 3). Hsp70s assist in protein refolding by binding of exposed hydrophobic surfaces of a substrate to a C-terminal peptide binding domain. Cycles of substrate binding and release are brought about by transition between low and high affinity binding states regulated by nucleotide occupancy in the N-terminal ATPase domain (4).In eukaryotic cells Hsp70 class chaperones can be divided into three subfamilies: 1) DnaK-like, 2) Hsp110, and 3) Grp170 (5). The budding yeast, Saccharomyces cerevisiae, possesses 14 Hsp70 homologs with family members present in the cytoplasm, endoplasmic reticulum (ER), and mitochondria (6). The most well studied Hsp70s in yeast are the cytoplasmic Ssa proteins (stress seventy A), encoded by the differentially expressed SSA1-4 genes. Ssa1-4 (collectively referred to as "Ssa") perform largely redundant functions and the presence of at least one SSA gene is required for viability (7). Ssa chaperones are involved in cellular processes such as translation, translocation of proteins across cellular membranes, and general protein folding (8). Cells depleted of Ssa exhibit multiple cellular defects, including: (i) growth arrest in G 2 /M phase, (ii) accumulation of precursor pr...

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Cns1 Is an Activator of the Ssa1 ATPase Activity

Cited by 46 publications

References 55 publications

Importance of the Hsp70 ATPase Domain in Yeast Prion Propagation

Importance of the Hsp70 ATPase Domain in Yeast Prion Propagation

SGT2 and MDY2 interact with molecular chaperone YDJ1 in Saccharomyces cerevisiae

The Yeast Hsp110 Sse1 Functionally Interacts with the Hsp70 Chaperones Ssa and Ssb

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