Functional domain analysis of the cell division inhibitor EzrA.

The precise spatial and temporal control of bacterial cell division is achieved through the balanced actions of factors that inhibit assembly of the tubulin-like protein FtsZ at aberrant subcellular locations or promote its assembly at the future sites of division. In Bacillus subtilis， the membrane anchored cell division protein EzrA， interacts directly with FtsZ to prevent aberrant FtsZ assembly at cell poles and contributes to the inherently dynamic nature of the cytokinetic ring. Recent work suggests EzrA also serves as a scaffolding protein to coordinate lateral growth with cell wall biosynthesis through interactions with a host of proteins， a finding consistent with EzrA's four extensive coiled-coil domains. In a previous study we identified a conserved patch of residues near EzrA's C-terminus (the QNR motif) that are critical for maintenance of a dynamic cytokinetic ring， but dispensable for EzrA-mediated inhibition of FtsZ assembly at cell poles. In an extension of this work， here we report that EzrA's two C-terminal coiled-coils function in concert with the QNR motif to mediate interactions with FtsZ and maintain the dynamic nature of the cytokinetic ring. In contrast， EzrA's two N-terminal coiled-coils are dispensable for interaction between EzrA and FtsZ in vitro and in vivo， but required for EzrA mediated inhibition of FtsZ assembly at cell poles. Finally， chimeric analysis indicates that EzrA's transmembrane anchor plays a generic role: concentrating EzrA at the plasma membrane where presumably it can most effectively modulate FtsZ assembly.