Replacement of GroEL in Escherichia coli by the group II chaperonin from the archaeon Methanococcus maripaludis

Chaperonins are required for correct folding of many proteins. They exist in two phylogenetic groups: Group I, found in bacteria and eukaryotic organelles, and Group II, found in archaea and eukaryotic cytoplasm. The two groups, while homologous, differ in significantly in structure and mechanism. Evolution of group II chaperonins has been proposed to have been key in enabling the expansion of the proteome required for eukaryotic evolution. In an archaeal species which expresses both groups of chaperonins, client selection is determined by structural and biochemical properties, rather than phylogenetic origin. It is thus predicted that Group II chaperonins will be poor at replacing Group I chaperonins. We have tested this hypothesis, and report here that the Group II chaperonin from M. maripaludis (Mm-cpn) can partially functionally replace GroEL, the Group I chaperonin of E. coli. Furthermore, we identify and characterise two single point mutations in Mm-cpn that have an enhanced ability to replace GroEL function, including one that allows E. coli growth after deletion of the groEL gene. The biochemical properties of the wild-type and mutant Mm-cpn proteins are reported. This shows that the two groups are not as functionally diverse as has been thought, and provides a novel platform for genetic dissection of Group II chaperonins.