Role of C-terminal extensions of subunits beta 2 and beta 7 in assembly and activity of eukaryotic proteasomes

• Autor(a) principal: Ramos, Paula C
• Data de Publicação: 2004
• Outros Autores: Marques, AJ, London, MK, Dohmen, RJ
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/11122
• topic: Mammalian 20S proteasome; Saccharomyces-Cerevisiae; Site formation; Yeast; Maturation; Resolution; Particle; Acidophilum; Propeptides; Completion

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.