MinC-MinD Copolymers Capture FtsZ Filaments to Facilitate the Regulation of Z-Ring Localization

Abstract

Self-organized MinDE proteins act as a dynamic reaction-diffusion device leading to their oscillation in vivo and facilitate to localize the bacterial contractile ring (Z ring) at the center of the cell. The previous model is set up by a feedback loop of the ATPase MinD and its activator MinE. MinC, an inhibitor of FtsZ polymerization, binds MinD and is carried as a passenger. However, MinC in vivo is around 0.7 μM, which is 6-8 times less than FtsZ and MinD; it contradicts the previous results that only excess MinC could affect FtsZ polymerization significantly. The recent results suggested that MinC and MinD could assemble into copolymers with 1:1 stoichiometry. However, the proposal was challenged since the previous study showed that the assembly of MinC-MinD required a high concentration of proteins and had a long lag time. We discovered new features of the coassembly of MinC-MinD from Pseudomonas aeruginosa. MinD alone dominates two properties of coassembly: critical concentration and lag time. If MinD is above ∼4 μM, it will copolymerize any low concentration MinC. The long lag time is also due to slow MinD dimerization: premixing MinD with ATP eliminated it all. It fits in vivo data well. Also, MinCD copolymers could bind FtsZ filaments and form huge bundles quickly and be disassembled by MinE protein. Based on these results, we propose a new “capture” model. Most MinC in vivo co-assembles with MinD into short copolymers quickly, and they will capture FtsZ filaments diffused away from the center. These tight bindings will let MinC shorten FtsZ filaments. The bound FtsZ filaments will be released after GTP is used up. It can explain why so low concentration MinC can regulate Z-ring formation.