title: Chaperonin GroEL uses asymmetric and symmetric reaction cycles in response to the concentration of non-native substrate proteins.
abstract: TheEscherichia colichaperonin GroEL is an essential molecular chaperone that mediates protein folding in association with its cofactor, GroES. It is widely accepted that GroEL alternates the GroES-sealed folding-active rings during the reaction cycle. In other words, an asymmetric GroEL-GroES complex is formed during the cycle, whereas a symmetric GroEL-(GroES)2complex is not formed. However, this conventional view has been challenged by the recent reports indicating that such symmetric complexes can be formed in the GroEL-GroES reaction cycle. In this review, we discuss the studies of the symmetric GroEL-(GroES)2complex, focusing on the molecular mechanism underlying its formation. We also suggest that GroEL can be involved in two types of reaction cycles (asymmetric or symmetric) and the type of cycle used depends on the concentration of non-native substrate proteins.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Iizuka
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Funatsu
keywords: molecular chaperone; protein folding; protein–protein interaction