The cytoplasmic Hsp70 chaperone machinery subjects misfolded and endoplasmic reticulum import-incompetent proteins to degradation via the ubiquitin-proteasome system.
The mechanism of protein quality control and elimination of misfolded proteins in the cytoplasm is poorly understood. We studied the involvement of cytoplasmic factors required for degradation of two endoplasmic reticulum (ER)-import-defective mutated derivatives of carboxypeptidase yscY (DeltassCPY* and DeltassCPY*-GFP) and also examined the requirements for degradation of the corresponding wild-type enzyme made ER-import incompetent by removal of its signal sequence (DeltassCPY). All these protein species are rapidly degraded via the ubiquitin-proteasome system. Degradation requires the ubiquitin-conjugating enzymes Ubc4p and Ubc5p, the cytoplasmic Hsp70 Ssa chaperone machinery, and the Hsp70 cochaperone Ydj1p. Neither the Hsp90 chaperones nor Hsp104 or the small heat-shock proteins Hsp26 and Hsp42 are involved in the degradation process. Elimination of a GFP fusion (GFP-cODC), containing the C-terminal 37 amino acids of ornithine decarboxylase (cODC) directing this enzyme to the proteasome, is independent of Ssa1p function. Fusion of DeltassCPY* to GFP-cODC to form DeltassCPY*-GFP-cODC reimposes a dependency on the Ssa1p chaperone for degradation. Evidently, the misfolded protein domain dictates the route of protein elimination. These data and our further results give evidence that the Ssa1p-Ydj1p machinery recognizes misfolded protein domains, keeps misfolded proteins soluble, solubilizes precipitated protein material, and escorts and delivers misfolded proteins in the ubiquitinated state to the proteasome for degradation.
Park
Sae-Hun
SH
Institut fuer Biochemie, Universitaet Stuttgart, 70569 Stuttgart, Germany.
Bolender
Natalia
N
Eisele
Frederik
F
Kostova
Zlatka
Z
Takeuchi
Junko
J
Coffino
Philip
P
Wolf
Dieter H
DH
D000251:Adenosine Triphosphatases / Q000378:metabolism; D002268:Carboxypeptidases / Q000737:chemistry* / Q000378:metabolism*; D043402:Cathepsin A; D003593:Cytoplasm / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C070319:YDJ1 protein, S cerevisiae; D002268:Carboxypeptidases; D043402:Cathepsin A; C499283:PRC1 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C095973:SSA1 protein, S cerevisiae