GroE prevents the accumulation of early folding intermediates of pre-.beta.-lactamase without changing the folding pathway

Abstract

In folding studies of pre-beta-lactamase in the presence of GroE, we investigated the pH dependence of the folding reaction. Two critical intermediates in the folding pathway were defined kinetically. I1 is an early folding intermediate recognized by GroE; the misfolding of I1 leads to aggregation, and this is prevented by GroE. A second intermediate I2 is released from GroE after ATP hydrolysis. Its pH-dependent misfolding to a nonnative form, which is not an aggregate, is not prevented by GroE. From these results, a model is proposed, in which the crucial role of GroE consists of allowing the change from I1 to I2 to take place in the complex. Fluorescence spectra of the pre-beta-lactamase complexed to GroE are very similar to those of the native state. The pathway of pre-beta-lactamase folding is not changed by GroE as evidenced by the same half-time and pH dependence of the folding reaction. GroE probably recognizes the signal sequence and some portion of the mature protein since mature beta-lactamase does not interact with GroE even under conditions of slow folding.