Comparative biochemical characterization of two GroEL homologs from the cyanobacterium Synechococcus elongatus PCC 7942.

Unlike Escherichia coli, cyanobacteria generally contain two GroEL homologs. The chaperone function of cyanobacterial GroELs was examined in vitro for the first time with GroEL1 and GroEL2 of Synechococcus elongatus PCC 7942. Both GroELs prevented aggregation of heat-denatured proteins. The ATPase activity of GroEL1 was approximately one-sixth that of Escherichia coli GroEL, while that of GroEL2 was insignificant. The activities of both GroELs were enhanced by GroES, while that of Escherichia coli GroEL was suppressed. The ATPase activity of GroEL1 was greatly enhanced in the presence of GroEL2, but the folding activities of GroEL1 and GroEL2 were much lower than that of Escherichia coli GroEL, regardless of the co-presence of the counterpart or GroES. Both native and recombinant GroEL1 forms a tetradecamer like Escherichia coli GroEL, while GroEL2 forms a heptamer or dimer, but the GroEL1 and GroEL2 oligomers were extremely unstable. In sum, we concluded that the cyanobacterial GroELs are mutually distinct and different from Escherichia coli GroEL.