Role of C-terminal extensions of subunits beta2 and beta7 in assembly and activity of eukaryotic proteasomes.

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.
Mesh Terms:
Amino Acid Sequence, Binding Sites, Cysteine Endopeptidases, Endopeptidases, Hydrogen Bonding, Molecular Chaperones, Molecular Sequence Data, Multienzyme Complexes, Mutagenesis, Peptide Hydrolases, Proteasome Endopeptidase Complex, Protein Structure, Tertiary, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins
J. Biol. Chem.
Date: Apr. 02, 2004
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