The Escherichia coli heat shock proteins GroEL and GroES modulate the folding of the beta-lactamase precursor

Abstract

One of the fundamental problems in biochemistry is the role of accessory proteins in the process of protein folding. The Escherichia coli heat shock protein complex GroEL/ES has been suggested to be a 'chaperonin' and be involved in both oligomer assembly as well as protein transport through the membrane. We show here that the folding of the purified precursor of beta-lactamase is inhibited by purified GroEL or the GroEL/ES complex with a stoichiometry of one particle per molecule of pre-beta-lactamase. Purified GroES alone has no effect on folding. After Mg2+ ATP addition folding resumes and the yield of active enzyme is higher than in the absence of GroEL or GroEL/ES. Unexpectedly, GroEL or GroEL/ES, when added to folded pre-beta-lactamase, lead to an apparent net 'unfolding', probably to a collapsed state of the protein, which can be reversed by the addition of Mg2+ ATP. The reversible and Mg2+ ATP-dependent association of GroEL/ES with non-native proteins might explain its postulated role in both protein transport and oligomer assembly.