ZapA uses a two‐pronged mechanism to facilitate Z ring formation in Escherichia coli

The tubulin‐like protein FtsZ assembles into the Z ring that leads to the assembly and activation of the division machinery in most bacteria. ZapA, a widely conserved protein that interacts with FtsZ, plays a pivotal role in organizing FtsZ filaments into a coherent Z ring. Previous studies revealed that ZapA forms a dumbbell‐like tetramer that binds cooperatively to FtsZ filaments and aligns them in parallel, leading to the straightening and organization of FtsZ filament bundles. However, how ZapA interacts with FtsZ remains obscure. Here, we reveal that ZapA uses a two‐pronged mechanism to interact with FtsZ to facilitate Z ring formation in Escherichia coli. We find that mutations affecting surface‐exposed residues at the junction between adjacent FtsZ subunits in a filament as well as in an N‐terminal motif of FtsZ weaken its interaction with ZapA in vivo and in vitro, indicating that ZapA binds to these regions of FtsZ. Consistent with this, ZapA prefers FtsZ polymers over monomeric FtsZ molecules and site‐specific crosslinking confirmed that the dimer head domain of ZapA is in contact with the junction of FtsZ subunits. As a result, disruption of the putative interaction interfaces between FtsZ and ZapA abolishes the midcell localization of ZapA. Taken together, our results suggest that ZapA tetramers grab the N‐terminal tails of FtsZ and bind to the junctions between FtsZ subunits in the filament to straighten and crosslink FtsZ filaments into the Z ring.