FUNCTIONAL-SIGNIFICANCE OF SYMMETRICAL VERSUS ASYMMETRICAL GROEL-GROES CHAPERONIN COMPLEXES

The Escherichia coli chaperonin GroEL and its regulator GroES are thou ght to mediate adenosine triphosphate-dependent protein folding as an asymmetrical complex, with substrate protein bound within the GroEL cy linder. In contrast, a symmetrical complex formed between one GroEL an d two GroES oligomers, with substrate protein binding to the outer sur face of GroEL, was recently proposed to be the functional chaperonin u nit. Electron microscopic and biochemical analyses have now shown that unphysiologically high magnesium concentrations and increased pH are required to assemble symmetrical complexes, the formation of which pre cludes the association of unfolded polypeptide. Thus, the functional s ignificance of GroEL:(GroES)(2) particles remains to be demonstrated.