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

Abstract

Bacterial 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 like <i>Streptomyces</i> and <i>Mycobacterium</i> lack 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 in <i>Streptomyces venezuelae</i> and that it binds FtsZ via a conserved helix-turn-helix motif, stimulating the assembly of FtsZ protofilaments. Comparative <i>in vitro</i> studies using the SepH homolog from <i>Mycobacterium smegmatis</i> further reveal that SepH can also bundle FtsZ protofilaments, indicating an additional Z-ring stabilizing function <i>in vivo</i>. We propose that SepH plays a crucial role at the onset of cytokinesis in actinobacteria by promoting the assembly of FtsZ filaments into division-competent Z-rings that can go on to mediate septum synthesis.