Hsp90 of <i>E. coli</i> modulates assembly of FtsZ, the bacterial tubulin homolog.

Abstract

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 <i>Escherichia coli</i>, Hsp90 causes cell filamentation when expressed at high levels. Here, we have explored the cause of filamentation and identified a potentially important client of <i>E. coli</i> 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 overexpressing 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 <i>E. coli</i> deleted for the Hsp90_Ec gene <i>htpG</i> turn over FtsZ more rapidly than wild-type cells. Additionally, the length of Δ<i>htpG</i> 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.