Mid-cell localization of the cell division septum in bacteria such as E. coli is controlled by a set of proteins including MinC, MinD, MinE, and FtsZ. FtsZ is the first structural component of the septum to polymerize on the inner membrane at the mid-cell when the cell starts to divide. FtsZ polymerization is limited to mid-cell by the action of the three Min proteins. MinC is an inhibitor of FtsZ polymerization, but on its own, it does not exhibit specific membrane localization. Instead, it binds to MinD, which is an ATP-dependent membrane binding protein, and the two proteins co-localize on the membrane. MinE interacts with MinD and controls MinD ATPase activity and also influences its membrane interaction, and hence its membrane association/dissociation dynamics. In vivo imaging studies have demonstrated the oscillating pattern formation of these two proteins, resulting in a concentration minimum of MinD, and hence MinC, at the mid-cell region when averaged over time. This observation explained why FtsZ polymerization is restricted to mid-cell. However, a detailed molecular mechanism of this bio-patterning reaction system is still poorly understood, due in part to the absence of a suitable cell-free reaction system to study this pattern formation reaction in detail. This project aims to investigate the biochemical and biophysical mechanism of the dynamic aspects of this reaction system by combining a variety of techniques, including the establishment and exploitation of a cell-free reaction system that recapitulates the in vivo system dynamics. Techniques and instruments have been developed to study these dynamic reaction systems in vitro by using a sensitive fluorescence microscope/CCD camera system. By using fluorescence-labeled MinD and MinE proteins, assembly and disassembly of these proteins on a supported lipid bilayer on the slide glass surface are monitored under a variety of reaction conditions. We successfully reconstituted a number of inter-converting modes of self-organized dynamic pattern formation by the two proteins in the presence of ATP on the membrane surface. Mechanistic details of the dynamic pattern organization are currently studied. The reaction system studied here is an example of a biomolecular patterning reaction, and the experimental techniques developed here will be exploited for parallel studies of mechanistically related reaction systems.

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Sundararajan, Kousik; Vecchiarelli, Anthony; Mizuuchi, Kiyoshi et al. (2018) Species- and C-terminal linker-dependent variations in the dynamic behavior of FtsZ on membranes in vitro. Mol Microbiol 110:47-63
Vecchiarelli, Anthony G; Li, Min; Mizuuchi, Michiyo et al. (2016) Membrane-bound MinDE complex acts as a toggle switch that drives Min oscillation coupled to cytoplasmic depletion of MinD. Proc Natl Acad Sci U S A 113:E1479-88
Vecchiarelli, Anthony G; Li, Min; Mizuuchi, Michiyo et al. (2014) Differential affinities of MinD and MinE to anionic phospholipid influence Min patterning dynamics in vitro. Mol Microbiol 93:453-63
Ivanov, Vassili; Mizuuchi, Kiyoshi (2010) Multiple modes of interconverting dynamic pattern formation by bacterial cell division proteins. Proc Natl Acad Sci U S A 107:8071-8