Conformational changes in the 20S proteasome upon macromolecular ligand binding analyzed with monoclonal antibodies

Proteasomes interact with a variety of macromolecular ligands that modulate their ability to degrade peptide and protein substrates, The effector PA28 increases the peptidase activities of proteasomes whereas HSP90 and alpha- crystallin inhibit a peptide-hydrolyzing activity. Four monoclonal antibodi es were used as probes to detect conformational changes of proteasome subun its. Conformational changes in alpha- or beta-subunits were found upon bind ing PA28, HSP90, alpha-crystallin, and the substrate casein but not with th e peptide substrate analogs calpain inhibitor 1 (Ac-Leu-Leu-norleucinal), c alpain inhibitor 2 (Ac-Leu-Leu-methioninal), or MG 132 (N-Cbz-Leu-Leu-leuci nal), (C) 1999 Academic Press.