ZapC promotes assembly and stability of FtsZ filaments by binding at a different site on FtsZ than ZipA

ZapC, a component of the divisome in Escherichia coli, is known to co-localize with FtsZ at the mid-cell position. A deletion or an overexpression of ZapC has been found to induce elongation of bacterial cells implying a role of ZapC in the cell division. ZapC has also been shown to enhance the assembly of purified FtsZ. In this study, ZapC was found to prevent the dilution-induced disassembly of preformed FtsZ polymers and to decorate FtsZ protofilaments along the length. ZapC interacted with FtsZ with a dissociation constant of 30 ± 7 nM. Salt had no discernable effect on the binding of ZapC to FtsZ; however, bis-ANS inhibited the binding of ZapC to FtsZ suggesting that the interaction was predominantly hydrophobic in nature. Several of the positive regulators of FtsZ assembly including ZipA are shown to bind FtsZ at the C-terminal tail of FtsZ. Using a 12-residue C-terminal tail peptide (LDIPAFLRKQAD) of FtsZ and a C-terminal tail truncated FtsZ construct, we provided data suggesting that ZapC does not bind at the C-terminal tail of FtsZ. The results indicated that ZapC and ZipA, two functionally similar proteins of the divisome complex, regulate FtsZ assembly through different sites of action on FtsZ.