Intraring allostery controls the function and assembly of a hetero-oligomeric class II chaperonin

Abstract

Class II chaperonins are essential multisubunit complexes that aid the folding of nonnative proteins in the cytosol of archaea and eukarya. They use energy derived from ATP to drive a series of structural rearrangements that enable polypeptides to fold within their central cavity. These events are regulated by an elaborate allosteric mechanism in need of elucidation. We employed mutagenesis and experimental analysis in concert with in silico molecular dynamics simulations and interface-binding energy calculations to investigate the class II chaperonin from Thermoplasma acidophilum. Here we describe the effects on the asymmetric allosteric mechanism and on hetero-oligomeric complex formation in a panel ofmutants in the ATP-binding pocket of the a and b subunits. Our observations reveal a potential model for a nonconcerted folding mechanism optimized for protecting and refolding a range of nonnative substrates under different environmental conditions, starting to unravel the role of subunit heterogeneity in this folding machine and establishing important links with the behavior of the most complex eukaryotic chaperonins.