SYMMETRICAL GROEL-GROES COMPLEXES CAN CONTAIN SUBSTRATE SIMULTANEOUSLY IN BOTH GROEL RINGS

Incubation of rhodanese with hche aperonins GroEL and GroES (1:2 GroEL (14):GroES(7) molar ratio) under functional and steady state condition s for ATP leads to the formation of a high proportion of rhodanese-bou nd symmetric complexes (GroEL(14)(GroES(7))(2)), as revealed by native electrophoresis. Aliquots of such samples were observed under the ele ctron microscope, and the symmetric particles were classified using ne uronal networks and multivariate statistical analysis. Three different populations of symmetric particles mere obtained which contained subs trate in none, one or both GroEL cavities, respectively. The presence of substrate in the symmetric complexes under functional conditions su pports 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 eff iciency of the reaction. (C) 1997 Federation of European Biochemical S ocieties.