Biochemistry

Proteosome Activators and Regulators

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Science  01 Dec 2000:
Vol. 290, Issue 5497, pp. 1653
DOI: 10.1126/science.290.5497.1653b

The proteasome is a barrel-shaped macromolecular complex and functions to degrade proteins into small peptides. Sousa et al. have determined the structure of viral HslUV; HslU, a chaperone of the Clp/Hsp100 family, is an ATP-dependent activator of the HslV protease. Two hexameric HslU molecules bind to opposite sides of HslV with the HslU intermediate domains (magenta) extending outward. This quartenary structure differs from that determined previously for a bacterial HslUV complex. Binding of HslU induces a shift in the apical helices of HslV that propagates to the active site.

In eukaryotes, apart from binding a 19S ATP-dependent regulator, the 20S proteasome also can bind to an 11S regulator, which appears to stimulate the release of peptides. Whitby et al. have determined the structure of the trypanosome 11S regulator bound to the 20S proteasome from yeast. They found that binding of the 11S regulator opened the pore, consistent with facilitating product export. This could result in the release of longer peptides and thus explain the role of 11S regulators in producing ligands for MHC class I molecules. — VV

Cell103, 633 (2000); Nature408, 115 (2000).

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