Evolution of Bacterial Chaperonin 60 Paralogues and Moonlighting Activity
Around two thirds of genome sequenced bacteria encode one chaperonin 60 protein with the other third encoding between two and eight chaperonin 60 paralogues. A surprising finding is that these bacterial proteins have a wide, and growing, range of additional functions both within the bacterium, but principally when the Cpn60 protein exits the cell and exists on the bacterial cell wall or in the bacterium’s external milieu. These findings have occurred at the same time that it has been realised that bacterial Cpn60 proteins can assume lower oligomeric forms than that of the prototypic tetradecameric E. coli GroEL. It is possible that lower oligomeric forms of Cpn60 may more readily be secreted and interact with biopolymers in a distinct manner to that of the tetradecameric homologues and paralogues. How the Cpn60 moonlighting functions evolved is a key question to be addressed. To address this question we postulate that the chaperonin genes have been subject to different selective constraints over evolutionary time. Gene duplication, followed by sequence divergence, resulted in the evolution of paralogous Cpn60 proteins that have distinct moonlighting activities. Moreover, these functional variations might be acquired by incorporating chemically dissimilar substitutions at functionally important residues.
KeywordsApical Domain Equatorial Domain groEL Gene Intermediate Domain Argininosuccinate Lyase
We thank Payel Ghosh and Pooja Gupta for stimulating discussions. The work was financially supported by the Department of Biotechnology (DBT), India. AS is a senior research fellow funded by University Grants Commission, India and CMSK is a research associate funded by the DBT.
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