NUCLEOTIDE-DEPENDENT COMPLEX-FORMATION BETWEEN THE ESCHERICHIA-COLI CHAPERONINS GROEL AND GROES STUDIED UNDER EQUILIBRIUM CONDITIONS

Binding of heptameric GroES to the tetradecameric chaperonin GroEL in the absence or presence of nucleotides was investigated by analytical ultracentrifugation. In the absence of nucleotides, the association co nstant for the binding of GroES to GroEL, K-1, was found to be approxi mately equal to 3 x 10(5) M-1. The binding of a second GroES heptamer with only one-fourth the affinity of the first one can be neglected at subequimolecular concentrations relative to GroEL. Under these condit ions, mainly an asymmetric ''bullet''-shaped complex is formed [see al so Schmidt et al. (1994) Science 265, 656-659]. In the presence of ADP or ATP analogues such as ATP-gamma-S or AMP-PNP, the affinity to bind GroES increases by at least 2 orders of magnitude depending on the nu cleotide concentration. With increasing GroES:GroEL ratios in the pres ence of 1 mM ATP analogue, up to two GroES oligomers were bound to one GroEL oligomer, forming the symmetrical ''American football''-shaped complex with apparently high affinity for the first GroES ring and con siderably lower for the second one. These are the first results that p rovide an accurate and quantitative description of the equilibrium bet ween asymmetrical and symmetrical complexes at relatively high concent rations of GroEL and GroES that are proposed to exist in vivo. We sugg est that the increased affinity of GroEL for GroES plays a role in rel easing substrate proteins from the central cavity of GroEL after foldi ng under ''non-permissive'' conditions.