pH-mediated control of anti-aggregation activities of cyanobacterial and E. coli chaperonin GroELs

In contrast to Escherichia coli, cyanobacteria have multiple GroELs, the bacterial homologues of chaperonin/Hsp60. We have shown that cyanobacterial GroELs are mutually distinct and different from E. coli GroEL with which the paradigm for chaperonin structure/function has been established. However, little is known about regulation of cyanobacterial GroELs. This study investigated effect of pH (varied from 7.0 to 8.5) on chaperone activity of GroEL1 and GroEL2 from the cyanobacterium Synechococcus elongatus PCC7942 and E. coli GroEL. GroEL1 and GroEL2 showed pH dependency in suppression of aggregation of heat-denatured malate dehydrogenase, lactate dehydrogenase and citrate synthase. They exhibited higher anti-aggregation activity at more alkaline pHs. Escherichia coli GroEL showed a similar pH-dependence in suppressing aggregation of heat-denatured lactate dehydrogenase. No pH dependence was observed in all the GroELs when urea-denatured lactate dehydrogenase was used for anti-aggregation assay, suggesting that the pH-dependence is related to some denatured structures. There was no significant influence of pH on the chaperone activity of all the GroELs to promote refolding of heat-denatured malate dehydrogenase. It is known that pH in cyanobacterial cytoplasm increases by one pH unit following a shift from darkness to light, suggesting that the pH-change modulates chaperone activity of cyanobacterial GroEL1 and GroEL2.