title: Distinct Elements in the Proteasomal β5 Subunit Propeptide Required for Autocatalytic Processing and Proteasome Assembly.
abstract: Eukaryotic 20S proteasome assembly remains poorly understood. The subunits stack into four heteroheptameric rings; three inner-ring subunits (β1, β2, and β5) bear the protease catalytic residues and are synthesized with N-terminal propeptides. These propeptides are removed autocatalytically late in assembly. In Saccharomyces cerevisiae, β5 (Doa3/Pre2) has a 75-residue propeptide, β5pro, that is essential for proteasome assembly and can work in trans. We show that deletion of the poorly conserved N-terminal half of the β5 propeptide nonetheless causes substantial defects in proteasome maturation. Sequences closer to the cleavage site have critical but redundant roles in both assembly and self-cleavage. A conserved histidine two residues upstream of the autocleavage site strongly promotes processing. Surprisingly, although β5pro is functionally linked to the Ump1 assembly factor, trans-expressed β5pro associates only weakly with Ump1-containing precursors. Several genes were identified as dosage suppressors of trans-expressed β5pro mutants; the strongest encoded the β7 proteasome subunit. Previous data suggested that β7 and β5pro have overlapping roles in bringing together two half-proteasomes, but the timing of β7 addition relative to half-mer joining was unclear. Here we report conditions where dimerization lags behind β7 incorporation into the half-mer. Our results suggest that β7 insertion precedes half-mer dimerization, and the β7 tail and β5 propeptide have unequal roles in half-mer joining.
authors.affiliation: From the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.affiliation: From the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and.
authors.forename: Yanjie
authors.initials: Y
authors.lastname: Li
authors.affiliation: the Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637.
authors.forename: Cassandra S
authors.initials: CS
authors.lastname: Arendt
authors.affiliation: From the Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520 and. Electronic address: mark.hochstrasser@yale.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Hochstrasser
mesh_terms: D020816:Amino Acid Motifs; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; C110856:proteasome maturation protein; C080044:PRE2 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex
keywords: chaperone; propeptide; proteasome; protein assembly; protein degradation; ubiquitin