A comprehensive model of the structure and function of the FtsZ ring of Escherichia coli

Reproduction of prokaryotes by binary fission ends with cytokinesis, the physical splitting of the cell membrane and external cell components. The most important protein in this process--- present in nearly all prokaryotes--- is the protein FtsZ. It both provides the scaffolding (the Z-ring) upon which the complete cytokinetic machine is built and the physical force that splits the cell into two. The essentiality of FtsZs function makes it difficult to study the Z-ring, begging an experimental method for in vitro reconstitution. We have developed a novel, robust system for reconstruction and physical/physiological characterization of functional Z-rings. With this system, we found two modes of constriction of the ring: a turnover-independent mode and a turnover-dependent mode. These may correspond to the hypothesized "sliding" and "bending" models of constriction, respectively. Lastly, we developed a holistic model of the Z-ring as a liquid crystal-like material exhibiting nematic order, but were unable to detect birefringence in solutions of purified, assembled FtsZ filaments using traditional techniques. Modifications to the detection method are proposed to make detection of ordered states much more likely.