Schmidtke G, Emch S, Groettrup M, Holzhutter HG. Evidence for the existence of a non-catalytic modifier site of peptide hydrolysis by the 20 S proteasome.
J Biol Chem 2000;
275:22056-63. [PMID:
10806206 DOI:
10.1074/jbc.m002513200]
[Citation(s) in RCA: 75] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 20 S proteasome is an endoprotease complex that preferentially cleaves peptides C-terminal of hydrophobic, basic, and acidic residues. Recently, we showed that these specific activities, classified as chymotrypsin-like, trypsin-like, and peptidylglutamyl peptide-hydrolyzing (PGPH) activity, are differently affected by Ritonavir, an inhibitor of human immunodeficiency virus-1 protease. Ritonavir competitively inhibited the chymotrypsin-like activity, whereas the trypsin-like activity was enhanced. Here we demonstrate that the Ritonavir-mediated up-regulation of the trypsin-like activity is not affected by specific active site inhibitors of the chymo-trypsin-like and PGPH activity. Moreover, we show that the mutual regulation of chymotrypsin-like and PGPH activities by their substrates as described previously by a "cyclical bite-chew" model is not affected by selective inhibitors of the respective active sites. These data challenge the bite-chew model and suggest that effectors of proteasome activity can act by binding to non-catalytic sites. Accordingly, we propose a kinetic "two-site modifier" model that assumes that the substrate (or effector) may bind to an active site as well as to a second non-catalytic modifier site. This model appears to be valid as it describes the complex kinetic effects of Ritonavir very well. Since Ritonavir partially inhibits major histocompatibility complex class I restricted antigen presentation, the postulated modifier site may be required to coordinate the active centers of the proteasome for the production of class I peptide ligands.
Collapse