Coregulated assembly of actin-like FtsA polymers with FtsZ during Z-ring formation and division in Escherichia coli

Abstract

In Escherichia coli, the actin homolog FtsA localizes the cell division machinery, beginning with the Z-ring, to the cytoplasmic membrane through direct interaction with FtsZ. FtsZ polymers are first to assemble at the Z-ring at midcell, where they direct constriction and septation. While FtsZ polymerization is critical for establishing a functional Z-ring that leads to constriction, the assembly state of FtsA and the role of FtsA ATP utilization during division in E. coli remain unclear. Here, we show that ATP hydrolysis, FtsZ interaction, and phospholipid vesicle remodeling by FtsA are impaired by a substitution mutation at the predicted active site for hydrolysis. This mutation, Glu 14 to Arg, also impairs Z-ring assembly and division in vivo. To further investigate the role of phospholipid engagement and ATP utilization in regulating FtsA function, we characterized a truncated E. coli FtsA variant, FtsA(ΔMTS), which lacks the region at the C-terminus important for engaging the membrane and is defective for ATP hydrolysis. We show that E. coli FtsA(ΔMTS) forms ATP-dependent actin-like filaments and assembly is antagonized by FtsZ. Polymerization of FtsZ with GTP, or a non-hydrolyzable analog, blocks inhibition of ATP-dependent FtsA assembly, and instead favors coassembly of stable FtsA/FtsZ polymers. In the cell, FtsA/FtsZ coassembly is favored at midcell, where FtsZ polymerizes, and inhibited at regions where FtsZ polymers are destabilized by regulators, such as MinC at the poles or SlmA at the nucleoid. We show that MinC prevents recruitment of FtsZ, via FtsA, to phospholipids, suggesting that local interactions of MinC with FtsZ block membrane tethering and uncouple the Z-ring from its major membrane contact. During Z-ring formation, the coassembly of FtsZ polymers with FtsA is coordinated and is a critical early step in division. This step also serves as a checkpoint by responding to the suite of FtsZ assembly regulators in the cell that modulate Z-ring position and dynamics prior to initiating cell wall synthesis.