title: Role of C-terminal extensions of subunits beta2 and beta7 in assembly and activity of eukaryotic proteasomes.
abstract: A close inspection of the crystal structure of the yeast 20 S proteasome revealed that a prominent connection between the two beta-rings is mediated by the subunit beta7/Pre4. Its C-terminal extension intercalates between the beta1/Pre3 and beta2/Pup1 subunits on the opposite ring. We show that the interactions promoted by the beta7/Pre4 tail are important to facilitate the formation of 20 S particles from two half-proteasome precursor complexes and/or to stabilize mature 20 S proteasomes. The deletion of 19 residues from the beta7/Pre4 C terminus leads to an accumulation of half-proteasome precursor complexes containing the maturation factor Ump1. The C-terminal extension of beta7/Pre4, which forms several hydrogen bonds with beta1/Pre3, is in addition required for the post-acidic activity mediated by the latter subunit. Deletion of the C-terminal tail of beta7/Pre4 results in an inhibition of beta1/Pre3 propeptide processing and abrogation of post-acidic activity. Our data obtained with yeast strains that expressed the mature form of Pre3 lacking its propeptide suggest that interactions between the Pre4 C terminus and Pre3 stabilize a conformation of its active site, which is essential for post-acidic activity. Deletion of the C-terminal extension of beta2/Pup1, which wraps around beta3/Pup3 within the same beta-ring, is lethal, indicating that this extension serves an essential function in proteasome assembly or stability.
authors.affiliation: Departamento de Química e Bioquímica, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8000-117 Faro, Portugal.
authors.forename: Paula C
authors.initials: PC
authors.lastname: Ramos
authors.forename: António J
authors.initials: AJ
authors.lastname: Marques
authors.forename: Markus K
authors.initials: MK
authors.lastname: London
authors.forename: R Jürgen
authors.initials: RJ
authors.lastname: Dohmen
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010450:Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016296:Mutagenesis; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D029701:Saccharomyces cerevisiae Proteins; C110856:proteasome maturation protein; D010450:Endopeptidases; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; C086455:PRE3 protein, S cerevisiae; D046988:Proteasome Endopeptidase Complex; C479563:Pup1 protein, S cerevisiae