GroES in the asymmetric GroEL14-GroES7 complex exchanges via an associative mechanism

Paul M. Horowitz, George H. Lorimer, Jesse Ybarra

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10 Scopus citations


The interaction of the chaperonin GroEL14 with its cochaperonin GroES7 is dynamic, involving stable, asymmetric 1:1 complexes (GroES7·GroEL7-GroEL7) and transient, metastable symmetric 2:1 complexes [GroES7·GroEL7-GroEL7·GroES 7]. The transient formation of a 2:1 complex permits exchange of free GroES7 for GroES7 bound in the stable 1:1 complex. Electrophoresis in the presence of ADP was used to resolve free GroEL14 from the GroES7-GroEL14 complex. Titration of GroEL14 with radiolabeled GroES7 to molar ratios of 32:1 demonstrated a 1:1 limiting stoichiometry in a stable complex. No stable 2:1 complex was detected. Preincubation of the asymmetric GroES7·GroEL7-GroEL7 complex with excess unlabeled GroES7 in the presence of ADP demonstrated GroES7 exchange. The rates of GroES7 exchange were proportional to the concentration of unlabeled free GroES7. This concentration dependence points to an associative mechanism in which exchange of GroES7 occurs by way of a transient 2:1 complex and excludes a dissociative mechanism in which exchange occurs by way of free GroEL14. Exchange of radiolabeled ADP from 1:1 complexes was much slower than the exchange of GroES7. In agreement with recent structural studies, this indicates that conformational changes in GroEL14 following the dissociation of GroES7 must precede ADP release. These results explain how the GroEL14 cavity can become reversibly accessible to proteins under in vivo conditions that favor 2:1 complexes.

Original languageEnglish (US)
Pages (from-to)2682-2686
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - Mar 16 1999
Externally publishedYes

ASJC Scopus subject areas

  • General


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