Binding, encapsulation and ejection: Substrate dynamics during a chaperonin-assisted folding reaction

JOURNAL OF MOLECULAR BIOLOGY

卷:266

Article

Ranson, NA ; Burston, SG ; Clarke, AR

关键词: protein folding;    molecular chaperones;    chaperonins;    malate dehydrogenase;    protein aggregation;   

DOI  :  10.1006/jmbi.1996.0815

来源: Elsevier

【 摘 要 】

Mitochondrial malate dehydrogenase (mMDH) folds more rapidly in the presence of GroEL, GroES and Am than it does unassisted. The increase in folding rate as a function of the concentration of GroEL-ES reaches a maximum at a stoichiometry which is approximately equimolar (mMDH subunits:GroEL oligomer) and with an apparent dissociation constant K' for the GroE acceptor state of at least 1 x 10(-8) M. However, even at chaperonin concentrations which are 4000 x K', i.e. at negligible concentrations of free mMDH, the observed folding rate of the substrate remains at its optimum, showing not only that folding occurs in the chaperonin-mMDH complex but also that this rate is uninhibited by any interactions with sites on GroEL. Despite the ability of mMDH to fold on the chaperonin, trapping experiments show that its dwell time on the complex is only 20 seconds. This correlates with both the rate of Am turnover and the du ell time of GroES on the complex and is only similar to 5% of the time taken for the substrate to commit to the folded state. The results imply that ATP drives the chaperonin complex through a cycle of three functional states: (1) an acceptor complex in which the unfolded substrate is bound tightly; (2) an encapsulation state in which it is sequestered but direct protein-protein contact is lost so that folding can proceed unhindered; and (3) an ejector state which forces dissociation of the substrate whether folded or not. (C) 1997 Academic Press Limited.

【 授权许可】

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