Direct Interaction of HtpG with the DnaK Chaperone System in the Cyanobacterium Synechococcus sp. PCC 7942

Abstract

Hsp90 is an essential and a ubiquitous chaperone protein in the cytosol of eukaryotic cells. The phenotype of mutants of HtpG which is a prokaryotic homolog of Hsp90 had not been observed in Escherichia coli and Bacillus subtilis. However we showed that the htpG disruptant strain from the cyanobacterium Synechococcus sp. PCC 7942 was sensitive to heat shock, indicating an essential role of HtpG. In the present study, we show that HtpG interacts directly with DnaJ, a prokaryotic homolog of Hsp40, by biochemical experiments such as co-immunoprecipitation studies and genetic analysis of yeast two-hybrid assays. Hsp40 is one of the cochaperones of Hsp70. Cyanobacteria have DnaKs which are prokaryotic homologs of Hsp70. It is known that Hsp90 cooperates with Hsp70/Hsp40 in eukaryotic cells, thus HtpG may collaborate with the DnaK chaperone system in Cyanobacteria.