title: The yeast Hsp110 Sse1 functionally interacts with the Hsp70 chaperones Ssa and Ssb.
abstract: 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 alpha-factor into the endoplasmic reticulum. Like ssa mutants, we demonstrate that sse1delta cells accumulate prepro-alpha-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.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston, Texas 77030, USA.
authors.forename: Lance
authors.initials: L
authors.lastname: Shaner
authors.forename: Harald
authors.initials: H
authors.lastname: Wegele
authors.forename: Johannes
authors.initials: J
authors.lastname: Buchner
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Morano
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000483:Alleles; D003600:Cytosol / Q000378:metabolism; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D050957:HSP110 Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D050957:HSP110 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; C060153:KAR2 protein, yeast; C048632:MF(ALPHA)1 protein, S cerevisiae; D018832:Molecular Chaperones; D010455:Peptides; D011498:Protein Precursors; C542288:SSA2 protein, S cerevisiae; C095192:SSB1 protein, S cerevisiae; C494656:SSE1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C494470:SSB2 protein, S cerevisiae; C095973:SSA1 protein, S cerevisiae