A conserved cell division protein directly regulates FtsZ dynamics in filamentous and unicellular actinobacteria

AbstractBacterial cell division is driven by the polymerization of the GTPase FtsZ into a contractile structure, the so-called Z-ring. This essential process involves proteins that modulate FtsZ dynamics and hence the overall Z-ring architecture. Actinobacteria, likeStreptomycesandMycobacteriumlack known key FtsZ-regulators. Here we report the identification of SepH, a conserved actinobacterial protein that directly regulates FtsZ dynamics. We show that SepH is crucially involved in cell division inStreptomycesand that it binds FtsZ via a conserved helix-turn-helix motif, stimulating the assembly of FtsZ protofilaments. Comparativein vitrostudies using the SepH homolog fromMycobacteriumfurther reveal that SepH can also bundle FtsZ protofilaments, indicating an additional Z-ring stabilizing functionin vivo. We propose that SepH plays a crucial role at the onset of cytokinesis in actinobacteria by promoting the rapid assembly of FtsZ filaments into division-competent Z-rings that can go on to mediate septum synthesis.