Denatured proteins facilitate the formation of the football-shaped GroEL-(GroES)2 complex

The University of Tokyo, Bunkyo-ku, Japan.
Biochemical Journal (Impact Factor: 4.4). 04/2010; 427(2):247-54. DOI: 10.1042/BJ20091845
Source: PubMed

ABSTRACT Controversy exists over whether the chaperonin GroEL forms a GroEL-(GroES)2 complex (football-shaped complex) during its reaction cycle. We have revealed previously the existence of the football-shaped complex in the chaperonin reaction cycle using a FRET (fluorescence resonance energy transfer) assay [Sameshima, Ueno, Iizuka, Ishii, Terada, Okabe and Funatsu (2008) J. Biol. Chem. 283, 23765-23773]. Although denatured proteins alter the ATPase activity of GroEL and the dynamics of the GroEL-GroES interaction, the effect of denatured proteins on the formation of the football-shaped complex has not been characterized. In the present study, a FRET assay was used to demonstrate that denatured proteins facilitate the formation of the football-shaped complex. The presence of denatured proteins was also found to increase the rate of association of GroES to the trans-ring of GroEL. Furthermore, denatured proteins decrease the inhibitory influence of ADP on ATP-induced association of GroES to the trans-ring of GroEL. From these findings we conclude that denatured proteins facilitate the dissociation of ADP from the trans-ring of GroEL and the concomitant association of ATP and the second GroES.

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    • "Fig. 2. Analysis of GroEL/ES symmetric complexes by calibrated FRET. The fluorophore pairs Cy3/Cy5 (a) and IAEDANS/F5M (b) were used as FRET reporters[17] [18]. 140 nM "
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    ABSTRACT: The chaperonin GroEL, a cylindrical complex consisting of two stacked heptameric rings, and its lid-like cofactor GroES form a nano-cage in which a single polypeptide chain is transiently enclosed and allowed to fold unimpaired by aggregation. GroEL and GroES undergo an ATP-regulated interaction cycle that serves to close and open the folding cage. Recent reports suggest that the presence of non-native substrate protein alters the GroEL/ES reaction by shifting it from asymmetric to symmetric complexes. In the asymmetric reaction mode only one ring of GroEL is GroES-bound and the two rings function sequentially, coupled by negative allostery. In the symmetric mode both GroEL rings are GroES-bound and are folding active simultaneously. Here we find that the results of FRET-based assays recently used to quantify symmetric complexes depend strongly on the fluorophore pair used. We therefore developed a novel assay based on fluorescence cross-correlation spectroscopy to accurately measure GroEL:GroES stoichiometry. This assay avoids fluorophore labeling of GroEL and the use of GroEL cysteine mutants. Our results show that symmetric GroEL:GroES2 complexes are substantially populated only in the presence of non-foldable model proteins, such as α-lactalbumin and α-casein, which 'over-stimulate' the GroEL ATPase and uncouple the negative GroEL inter-ring allostery. In contrast, asymmetric complexes are dominant both in the absence of substrate and presence of foldable substrate proteins. Moreover, uncoupling of the GroEL rings and formation of symmetric GroEL:GroES2 complexes is suppressed at physiological ATP:ADP concentration. We conclude that the asymmetric GroEL:GroES complex represents the main folding active form of the chaperonin. Copyright © 2015. Published by Elsevier Ltd.
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