ATP induces large quaternary rearrangements in a cage-like chaperonin structure

H. R. Saibil, D. Zheng, A. M. Roseman, A. S. Hunter, G. M F Watson, S. Chen, A. Auf Der Mauer, B. P. O'Hara, S. P. Wood, N. H. Mann, L. K. Barnett, R. J. Ellis

    Research output: Contribution to journalArticlepeer-review


    Background: The chaperonins, a family of molecular chaperones, are large oligomeric proteins that bind non-native intermediates of protein folding. They couple the release and correct folding of their ligands to the binding and hydrolysis of ATP. Chaperonin 60 (cpn60) is a decatetramer (14-mer) of 60 kD subunits. Folding of some ligands also requires the cooperation of cpn10, a heptamer of 10 kD subunits. Results: We have determined the three-dimensional arrangements of subunits in Rhodobacter sphaeroides cpn60 in the nucleotide-free and ATP-bound forms. Negative stain electron microscopy and tilt reconstruction show the cylindrical structure of the decatetramer comprising two rings of seven subunits. The decatetramer consists of two cages joined base-to-base without a continuous central channel. These cages appear to contain bound polypeptide with an asymmetric distribution between the two rings. The two major domains of each subunit are connected on the exterior of the cylinder by a narrower bridge of density that could be a hinge region. Binding of ATP to cpn60 causes a major rearrangement of the protein density, which is reversed upon the hydrolysis of the ATP. Cpn10 binds to only one end of the cpn60 structure and is visible as an additional layer of density forming a cap on one end of the cpn60 cylinder. Conclusions: The observed rearrangement is consistent with an inward 5-10° rotation of subunits, pivoting about the subunit contacts between the two heptamers, and thus bringing cpn60 domains towards the position occupied by the bound polypeptide. This change could explain the stimulation of ATPase activity by ligands, and the effects of ATP on lowering the affinity of cpn60 for ligands and on triggering the release of folding polypeptides.
    Original languageEnglish
    Pages (from-to)265-273
    Number of pages8
    JournalCurrent Biology
    Issue number5
    Publication statusPublished - 1993


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