FtsEX acts on FtsA to regulate divisome assembly and activity.

Bacterial cell division is driven by the divisome, a ring-shaped protein complex organized by the bacterial tubulin homolog FtsZ. Although most of the division proteins in Escherichia coli have been identified, how they assemble into the divisome and synthesize the septum remains poorly understood. Recent studies suggest that the bacterial actin homolog FtsA plays a critical role in divisome assembly and acts synergistically with the FtsQLB complex to regulate the activity of the divisome. FtsEX, an ATP-binding cassette transporter-like complex, is also necessary for divisome assembly and inhibits division when its ATPase activity is inactivated. However, its role in division is not clear. Here, we find that FtsEX acts on FtsA to regulate both divisome assembly and activity. FtsX interacts with FtsA and this interaction is required for divisome assembly and inhibition of divisome function by ATPase mutants of FtsEX. Our results suggest that FtsEX antagonizes FtsA polymerization to promote divisome assembly and the ATPase mutants of FtsEX block divisome activity by locking FtsA in the inactive form or preventing FtsA from communicating with other divisome proteins. Because FtsEX is known to govern cell wall hydrolysis at the septum, our findings indicate that FtsEX acts on FtsA to promote divisome assembly and to coordinate cell wall synthesis and hydrolysis at the septum. Furthermore, our study provides evidence that FtsA mutants impaired for self-interaction are favored for division, and FtsW plays a critical role in divisome activation in addition to the FtsQLB complex.