title: A shunt pathway limits the CaaX processing of Hsp40 Ydj1p and regulates Ydj1p-dependent phenotypes.
abstract: The modifications occurring to CaaX proteins have largely been established using few reporter molecules (e.g. Ras, yeast a-factor mating pheromone). These proteins undergo three coordinated COOH-terminal events: isoprenylation of the cysteine, proteolytic removal of aaX, and COOH-terminal methylation. Here, we investigated the coupling of these modifications in the context of the yeast Ydj1p chaperone. We provide genetic, biochemical, and biophysical evidence that the Ydj1p CaaX motif is isoprenylated but not cleaved and carboxylmethylated. Moreover, we demonstrate that Ydj1p-dependent thermotolerance and Ydj1p localization are perturbed when alternative CaaX motifs are transplanted onto Ydj1p. The abnormal phenotypes revert to normal when post-isoprenylation events are genetically interrupted. Our findings indicate that proper Ydj1p function requires an isoprenylatable CaaX motif that is resistant to post-isoprenylation events. These results expand on the complexity of protein isoprenylation and highlight the impact of post-isoprenylation events in regulating the function of Ydj1p and perhaps other CaaX proteins.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: Emily R
authors.initials: ER
authors.lastname: Hildebrandt
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Cheng
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhao
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: June H
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: Lance
authors.identifier: 0000-0003-4956-5363
authors.initials: L
authors.lastname: Wells
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Georgia, Athens, United States.
authors.forename: Walter K
authors.identifier: 0000-0002-3359-3434
authors.initials: WK
authors.lastname: Schmidt
mesh_terms: D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism*; D054876:Prenylation; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*
chemical_list: D050956:HSP40 Heat-Shock Proteins; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae
keywords: CaaX; HSP40; S. cerevisiae; biochemistry; cell biology; chaperone; isoprenylation; thermotolerance