Formation of Proteasome−PA700 Complexes Directly Correlates with Activation of Peptidase Activity

The proteolytic activity of the eukaryotic 20S proteasome is stimulated by a multisubunit activator, PA700, which forms both 1:1 and 2:1 complexes with the proteasome. Formation of the complexes is enhanced by an additional protein assembly called modulator, which also stimulates the enzymatic activ...

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Bibliographic Details
Published in:	Biochemistry (Easton) Vol. 37; no. 37; pp. 12927 - 12932
Main Authors:	Adams, George M, Crotchett, Brad, Slaughter, Clive A, DeMartino, George N, Gogol, Edward P
Format:	Journal Article
Language:	English
Published:	United States American Chemical Society 15-09-1998
Subjects:	Animals Cattle Cysteine Endopeptidases - chemistry Cysteine Endopeptidases - metabolism Cysteine Endopeptidases - ultrastructure Endopeptidases - metabolism Enzyme Activation - drug effects Microscopy, Electron Multienzyme Complexes - chemistry Multienzyme Complexes - metabolism Multienzyme Complexes - ultrastructure Peptide Hydrolases - metabolism Proteasome Endopeptidase Complex Proteins - chemistry Proteins - metabolism Proteins - physiology Proteins - ultrastructure
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Summary:	The proteolytic activity of the eukaryotic 20S proteasome is stimulated by a multisubunit activator, PA700, which forms both 1:1 and 2:1 complexes with the proteasome. Formation of the complexes is enhanced by an additional protein assembly called modulator, which also stimulates the enzymatic activity of the proteasome only in the presence of PA700. Here we show that the binding of PA700 to the proteasome is cooperative, as is the activation of the proteasome's intrinsic peptidase activity. Modulator increases the extent of complex formation and peptidase activation, while preserving the cooperative kinetics. Furthermore, the increase in activity is not linear with the number of PA700 assemblies bound to the proteasome, but rather with the number of proteasome−PA700 complexes, regardless of the PA700:proteasome stoichiometry. Hence the stimulation of peptidase activity is fully (or almost fully) effected by the binding of a single PA700 to the 20S proteasome. The stimulation of peptidase by modulator is explained entirely by the increased number of proteasome−PA700 complexes formed in its presence, rather than by any substantial direct stimulation of catalysis. These observations are consistent with a model in which PA700, either alone or assisted by modulator, promotes conformational changes in the proteasome that activate the catalytic sites and/or facilitate access of peptide substrates to these sites.
Bibliography:	istex:5AA8703419B87EBA4EF858146BCC1FE47636FC43 This work was supported by grants from the University of Missouri Research Board and the National Insitutes of Health (GM57403 to E.P.G. and DK46181 to G.N.D.). ark:/67375/TPS-XPG7VLS1-K ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0006-2960 1520-4995
DOI:	10.1021/bi981482i