BIOCHEMICAL-CHARACTERIZATION OF SYMMETRICAL GROEL-GROES COMPLEXES - EVIDENCE FOR A ROLE IN PROTEIN-FOLDING

When chaperonins GroEL and GroES are incubated under functional condit ions in the presence of ATP (5 mM) and K+ (150 mM), GroEL-GroES comple xes appear in the incubation mixture, that are either asymmetric (1:1 GroEL:GroES oligomer ratio) or symmetric (1:2 GroEL:GroES oligomer rat io). The percentage of symmetric complexes present is directly related to the [ATP]/[ADP] ratio and to the K+ concentration. Kinetic analysi s shows that there is a cycle of formation and disappearance of symmet ric complexes. A correlation between the presence of symmetric complex es in the incubation mixture and its rhodanese folding activity sugges ts some active role of these complexes in the protein folding process. Accordingly, under functional conditions, symmetric complexes are fou nd to contain denatured rhodanese. These data suggest that binding of substrate inside the GroEL cavity takes place before the symmetric com plex is formed.