Colloquium20120306-Meso-scale intracellular molecular-patterning in bacteria: plasmid partition to c
Department of Physics, NCU
Meso-scale intracellular molecular-patterning in bacteria: plasmid partition to cell division septum positioning
Prof. Kiyoshi Mizuuchi
Laboratory of Molecular Biology, National Institutes of Health, National Institute of Diabetes, and Digestive and Kidney Diseases, USA
In bacteria, a family of Walker-type ATPases are involved in self-organized dynamic molecular pattern formation that controls cell division processes. We study several of these systems by using cell-free reconstituted reaction systems.
Bacterial chromosome and plasmid partition systems assure stable heritance of genomes, commonly involving a partition ATPase, “centromere”-like DNA site, and a “centromere”-binding protein that stimulates the partition ATPase, which is an ATP-dependent non-specific DNA binding protein. Plasmid P1 and F partition systems have been reconstituted using fluorescence-labeled components in a flow cell under a TIRF microscope. We will discuss the possible mechanism of plasmid partition based on our recent observations.
The mid-cell localization of cell division septum in E. coli is controlled by a set of Min proteins, which limits polymerization of FtsZ, the initiator of septation, to mid-cell. MinC inhibits FtsZ polymerization, and MinC distribution on the membrane is dictated by MinD to which it binds. MinD, a homologue of partition ATPases, is an ATP-dependent membrane binding protein, and MinE associates with membrane-bound MinD and controls its ATPase. Together, membrane-bound MinD (with MinC bound to it) and MinE oscillate between the cell poles in vivo. This generates time-averaged distribution minimum of MinC at the mid-cell, assuring the cell division at the mid-cell. We study self-organized MinD/E dynamics in a reconstituted cell-free system by using TIRF microscopy. The simple reaction-diffusion models previously proposed for the Min system fail to explain the results of in vitro self-organization experiments. We will discuss recent findings that shed light on the mechanistic aspects of the reaction mechanism that contribute to the spatio-temporal coordination of the membrane association and dissociation of the proteins that produces observed dynamic patterns.