Accepted post-doctoral position at Vanderbilt University after receiving PhD
Now employed as Associate Research Scientist, Dow Microbial Control at Dow Chemical, Philadelphia
Bacterial cell division is a complex process that relies on the intricate timing and placement of the FtsZ ring. FtsZ, the prokaryotic homologue of tubulin, assembles into the FtsZ ring at the cell midpoint and is proposed to provide a scaffold upon which the remaining cell division components localize. The resulting putative protein complex or divisome is required for the synthesis of the division septum and subsequent formation of new cell poles. Although most of the components of the cell division machinery have likely been identified, how this multi-subunit complex is assembled within the membrane, and the precise roles of each protein, have remained elusive. In addition, the mechanism for the selection of the division plane between the daughter chromosomes at the cell midpoint is also not well understood.
Our laboratory has made significant progress towards answering these questions as we have helped elucidate the role of two essential cell division proteins of Escherichia coli, FtsA and FtsE. Using a novel polar recruitment assay, we found that FtsA can recruit at least two late septation proteins, FtsI and FtsN, to the cell poles independently of FtsZ rings. Moreover, a unique structural domain of FtsA absent in the other ATPase superfamily members, domain 1c, is sufficient for this recruitment but not required for the ability of FtsA to localize to FtsZ rings. By conducting immuno-precipitation experiments, we were also able to identify a specific binary interaction between FtsZ and FtsE, part of a putative ABC transporter. This interaction is mediated by the N-terminus of FtsZ, and provides the first evidence of a domain of FtsZ, besides its extreme C-terminus, which is directly involved in recruiting downstream cell division components.
The MinCDE proteins help to select cell division sites in normal cylindrical E. coli by oscillating along the long axis, preventing unwanted polar divisions. To determine how the Min system might function in 3 dimensional space, we investigated its role in a round-cell rodA mutant. Round cells lacking MinCDE were viable, but growth, morphology and positioning of cell division sites were abnormal relative to Min+ cells. In round cells with a long axis, such as those undergoing cell division, green fluorescent protein (GFP) fusions to MinD almost always oscillated parallel to the long axis. However, round or irregularly shaped cells exhibited MinD movement to and from multiple sites on the cell surface. A MinE-GFP fusion also exhibited similar behavior. These results indicate that the Min proteins can potentially localize anywhere in the cell but tend to move a certain maximum distance from their previous assembly site, thus favoring movement along the cell’s long axis. Because rodA cells growing on solid media become kidney-shaped as a result of the deep medial constriction of the mother cell, they develop a long axis parallel to the last division plane, which should then set up a MinCD gradient that favors mid-cell division in the perpendicular plane. This could explain why cocci divide in alternating perpendicular planes.
Subcellular Targeting of and Protein-Protein Interactions within the Bacterial Cell Division Complex