Hsp90 of E. coli modulates assembly of FtsZ, the bacterial tubulin homolog

Heat shock protein 90 (Hsp90) is a highly conserved molecular chaperone involved in ATP-dependent client protein remodeling and activation. It also functions as a protein holdase, binding and stabilizing clients in an ATP-independent process. Hsp90 remodels over 300 client proteins and is essential for cell survival in eukaryotes. In bacteria, Hsp90 is a highly abundant protein, although very few clients have been identified and it is not essential for growth in many bacterial species. We previously demonstrated that in Escherichia coli, Hsp90 causes cell filamentation when expressed at high levels. Here, we have explored the cause of filamentation and identified a potentially important client of E. coli Hsp90 (Hsp90(Ec)), FtsZ. We observed that FtsZ, a bacterial tubulin homolog essential for cell division, fails to assemble into FtsZ rings (divisomes) in cells over-expressing Hsp90(Ec). Additionally, Hsp90(Ec) interacts with FtsZ and inhibits polymerization of FtsZ in vitro, in an ATP-independent holding reaction. The FtsZ-Hsp90(Ec) interaction involves residues in the client-binding region of Hsp90(Ec) and in the C-terminal tail of FtsZ, where many cell-division proteins and regulators interact. We observed that E. coli deleted for the Hsp90(Ec) gene htpG turn over FtsZ more rapidly than wild-type cells. Additionally, the length of Delta htpG cells is reduced compared to wild-type cells. Altogether, these results suggest that Hsp90(Ec) is a modulator of cell division, and imply that the polypeptide-holding function of Hsp90 may be a biologically important chaperone activity.