Structural Investigation Of The Molecular Chaperonin Tf55 From Thermophilic Archaeon Sulfolobus Solfataricus

Chaperonins are ubiquitous multi-subunit macromolecules that mediate the folding and assembly of certain proteins that cannot fold properly in vivo. The Archaea bacterium Sulfolobus solfataricus encodes for three chaperonin complexes formed from three different, but closely related subunits named alpha,betaand Gamma. These subunits form a homo-18mer composed of all beta subunits at temperatures ranging between 80oC-85oC, a hetero-16mer composed of alpha and beta subunits at temperatures ranging between 70oC-75oC and a hetero 18mer composed of alpha, beta and gamma subunits at temperatures of 60oC. Structures exist for the chaperonin TF55 all-beta complex and for the TF55 alpha-beta complex but not for the TF55 alpha-beta-gamma complex. Here we present the structural investigation of the chaperonin TF55 alpha-beta-gamma in the presence of ATP. The cryo-EM reconstruction of TF55 chaperonin complex revealed a double-ring of 18 subunits with nine subunits in each ring. Each of the subunits are arranged in an alternating fashion where three hetero-trimers reside in each ring and the intact 18-meric complex is formed by two of these rings stacked back to back, similar to other chaperonin complexes