Structural and functional characterization of homo-oligomeric complexes of alpha and beta chaperonin subunits from the hyperthermophilic archaeum Thermococcus strain KS-1.

To elucidate the function of group II chaperonin, the gene for the chaperonin from the hyperthermophilic archaeum Thermococcus strain KS-1 was cloned and sequenced. Two distinct genes coding for chaperonin subunits, designated alpha and beta, were obtained, and their deduced amino acid sequences are highly homologous to those of group II chaperonins from other sources. The alpha and beta subunits were individually expressed in Escherichia coli. Both of the recombinant subunits assemble to constitute the homo-oligomeric double-ring complexes, which are prone to form large aggregates. The alpha aggregate is dissociated into the typical chaperonin ring complex by incubation in buffer containing 15% (v/v) methanol, while the beta aggregate cannot be dissociated. At high temperature, both of the recombinant complexes have weak ATPase activities. They are able to arrest refolding of a chemically denatured thermophilic enzyme in the absence of ATP, and refolding is resumed when ATP is supplemented. These results suggest that homo-oligomeric complexes of the archaeal chaperonin have activity.