REVERSIBLE OLIGOMERIZATION AND DENATURATION OF THE CHAPERONIN GROES

The chaperonin GroEL can assist protein folding and normally acts with the co-chaperonin GroES. These Escherichia coli proteins are encoded on the same operon, with GroES positioned first. In this report, we ha ve investigated the reversible folding of GroES. Using fluorescence an isotropy of dansyl-labeled GroES, intrinsic fluorescence, bis-ANS bind ing, sedimentation velocity, and limited proteolysis, we show that Gro ES unfolds in a single, two-state transition. Importantly, intrinsic f luorescence and sedimentation velocity analyses show that GroES is cap able of refolding and reassembling from a urea denatured state. The re folded GroES is fully active as shown by its ability to assist GroEL i n the refolding of rhodanese. These results indicate that chaperonins may not require other chaperonins for successful folding/assembly. We also show that GroES is capable of assisting in the refolding/reassemb ly of fully denatured GroEL. The reversible folding of GroES coupled w ith the ability of GroES to assist the refolding/reassembly of GroEL s uggest that the groE operon may be organized in a manner that provides a structural role in GroES/GroEL assembly as well as a functional rol e.