Symmetric GroEL-GroES complexes can contain substrate simultaneously in both GroEL rings.

Incubation of rhodanese with hche aperonins GroEL and GroES (1:2 GroEL14:GroES7 molar ratio) under functional and steady state conditions for ATP leads to the formation of a high proportion of rhodanese-bound symmetric complexes (GroEL14(GroES7)2), as revealed by native electrophoresis. Aliquots of such samples were observed under the electron microscope, and the symmetric particles were classified using neuronal networks and multivariate statistical analysis. Three different populations of symmetric particles were obtained which contained substrate in none, one or both GroEL cavities, respectively. The presence of substrate in the symmetric complexes under functional conditions supports their role as active intermediates in the protein folding cycle. These results also suggest that symmetric GroEL-GroES complexes can use both rings simultaneously for folding, probably increasing the efficiency of the reaction.