The C-terminal domain of MinC, a cell division regulation protein, is sufficient to form a copolymer with MinD

Assembly of cell division protein FtsZ into the Z-ring at the division site is a key step in bacterial cell division. The Min proteins can restrict the Z-ring to the middle of the cell. MinC is the main protein that obstructs Z-ring formation by inhibiting FtsZ assembly. Its N-terminal domain (MinC^N ) regulates the localization of the Z-ring by inhibiting FtsZ polymerization, while its C-terminal domain (MinC^C ) binds to MinD as well as to FtsZ. Previous studies have shown that MinC and MinD form copolymers in vitro. This copolymer may greatly enhance the binding of MinC to FtsZ, and/or prevent FtsZ filaments from diffusing to the ends of the cell. Here, we investigated the assembly properties of MinC^C -MinD of Pseudomonas aeruginosa. We found that MinC^C is sufficient to form the copolymers. Although MinC^C -MinD assembles into larger bundles, most likely because MinC^C is spatially more readily bound to MinD, its copolymerization has similar dynamic properties: the concentration of MinD dominates their copolymerization. The critical concentration of MinD is around 3 μm and when MinD concentration is high enough, a low concentration MinC^C could still be copolymerized. We also found that MinC^C -MinD can still rapidly bind to FtsZ protofilaments, providing direct evidence that MinC^C also interacts directly with FtsZ. However, although the presence of minC^C can slightly improve the division defect of minC-knockout strains and shorten the cell length from an average of 12.2 ± 6.7 to 6.6 ± 3.6 μm, it is still insufficient for the normal growth and division of bacteria.