CHAPERONINS

Many proteins do not fold spontaneously into an active form under intracellular conditions, and the chaperonins are emerging as crucial elements mediating their correct assembly. Chaperonins are large multisubunit, cage-like proteins into which 'unfolded' polypeptides may be bound; these are subsequently released in correctly folded or folding-competent form, by a mechanism often coupled to ATP hydrolysis. Structural and biochemical studies of chaperonins are beginning to address their form and mode of action. Chaperonins exist in multiple conformations which are determined by the binding of nucleotides and substrate polypeptides.