Structure-function relationships in bovine thymus 20S proteasome: a fluorimetric study

The structure-function relationships occurring on the bovine thymus 20S pro teasome, which exhibits the features of an immunoproteasome, have been stud ied. The investigation has been performed, essentially, using a fluorimetri c approach, taking advantage either of the sensitivity of the complex to so dium dodecil sulfate and chaotropic agents (urea and guanidine hydrochlorid e) or of the presence, on the molecule, of a high number of tryptophan resi dues. The results obtained indicate that the perturbation or the oxidation of these residues affect the catalytic events taking place on the thymus pr oteasome and that the functional effects determined by SDS and chaotropic a gents most likely occur through a series of progressive structural modifica tions leading to an inactive molecule. The presence of structural intermedi ates in the proteasome inactivation process suggests that thymus proteasome is a molecule characterized, at the same time, by structural flexibility ( modulation of active sites) and structural stability (maintaining of the qu aternary structure) in agreement with its crucial role in the cell life cyc le. (C) 2001 Elsevier Science B.V. All rights reserved.