Structural insights into thermophilic chaperonin complexes

Group I chaperonins are dual heptamer protein complexes that play significant roles in protein homeostasis. The structure and function of the Escherichia coli chaperonin are well characterized. However, the dynamic properties of chaperonins, such as large ATPase-dependent conformational changes by binding of lid-like co-chaperonin GroES, have made structural analyses challenging, and our understanding of these changes during the turnover of chaperonin complex formation is limited. In this study, we used single-particle cryogenic electron microscopy to investigate the structures of GroES-bound chaperonin complexes from the thermophilic hydrogen-oxidizing bacteria Hydrogenophilus thermoluteolus and Hydrogenobacter thermophilus in the presence of ATP and AMP-PNP. We captured the structure of an intermediate state chaperonin complex, designated as an asymmetric football-shaped complex, and performed analyses to decipher the dynamic structural variations. Our structural analyses of inter- and intra-subunit communications revealed a unique mechanism of complex formation through the binding of a second GroES to a bullet-shaped complex. [Display omitted] •Cryo-EM structures of chaperonin complexes from two thermophilic bacteria•The asymmetric football structure is an intermediate state during trans-GroES binding•Dynamics of trans-GroEL during interaction with GroES were elucidated Chaperonins play significant roles in protein homeostasis, but their dynamic properties are not well understood. Liao et al. investigated cryo-EM structures of the GroELS complex from two thermophilic hydrogen-oxidizing bacteria. An asymmetric football-shaped complex was captured and analyzed as an intermediate state during the full complex formation.