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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 6; pp. 2682 - 2686
• Main Authors: Horowitz, P M, Lorimer, G H, Ybarra, J
• Format: Journal Article
• Language: English
• Published: United States National Acad Sciences 16-03-1999; National Academy of Sciences; The National Academy of Sciences
• Subjects: Biochemistry; Biological Sciences; Chaperonin 10 - chemistry; Chaperonin 10 - metabolism; Chaperonin 60 - chemistry; Chaperonin 60 - metabolism; Escherichia coli - chemistry; Escherichia coli - metabolism; Molecules; Protein Binding; Proteins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.6.2682

The interaction of the chaperonin GroEL 14 with its cochaperonin GroES 7 is dynamic, involving stable, asymmetric 1:1 complexes (GroES 7 ⋅GroEL 7 –GroEL 7 ) and transient, metastable symmetric 2:1 complexes [GroES 7 ⋅GroEL 7 –GroEL 7 ⋅GroES 7 ]. The transient formation of a 2:1 complex permits exchange of free GroES 7 for GroES 7 bound in the stable 1:1 complex. Electrophoresis in the presence of ADP was used to resolve free GroEL 14 from the GroES 7 –GroEL 14 complex. Titration of GroEL 14 with radiolabeled GroES 7 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 GroES 7 ⋅GroEL 7 –GroEL 7 complex with excess unlabeled GroES 7 in the presence of ADP demonstrated GroES 7 exchange. The rates of GroES 7 exchange were proportional to the concentration of unlabeled free GroES 7 . This concentration dependence points to an associative mechanism in which exchange of GroES 7 occurs by way of a transient 2:1 complex and excludes a dissociative mechanism in which exchange occurs by way of free GroEL 14 . Exchange of radiolabeled ADP from 1:1 complexes was much slower than the exchange of GroES 7 . In agreement with recent structural studies, this indicates that conformational changes in GroEL 14 following the dissociation of GroES 7 must precede ADP release. These results explain how the GroEL 14 cavity can become reversibly accessible to proteins under in vivo conditions that favor 2:1 complexes.