Abstract
HSP90/HtpG constitutes one of the most abundant and conserved heat-shock protein (HSP) families. Compared with HSP90 in eukaryotes, little is known about a role for the HSP90 homologues in prokaryotes due to the lack of a mutant that shows a clear phenotype under stress conditions.
Previously, we showed that the inactivation of the htpG gene from the cyanobacterium Synechococcus sp. PCC 7942 causes loss in thermotolerance, indicating an indispensable role of HtpG for the survival under heat stress.
In the present study, we over-expressed the cyanobacterial htpG gene in E. coli and purified the HtpG protein. HtpG forms a homo-dimer and prevented the irreversible aggregation of a model substrate such as citrate synthase by heat. On the other hand, a truncated form of HtpG lacking the C-terminal 124 amino acids could not form an oligomer, indicating that the region is important for the oligomer formation.
