The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences Dissertations and Theses (Open Access)
ORGANIZATION AND REGULATION OF PROTEINS REQUIRED FOR INITIATION OF CELL DIVISION IN ESCHERICHIA COLI
Date of Graduation
Microbiology and Molecular Genetics
Doctor of Philosophy (PhD)
William Margolin, Ph.D.
Kevin A. Morano, Ph.D.
Theresa M. Koehler, Ph.D.
Heidi B. Kaplan, Ph.D.
Joseph L. Alcorn, Ph.D.
The process of bacterial cell division relies on the assembly of multiple proteins to form the cell division machine, or “divisome.” FtsZ, a bacterial homolog of eukaryotic tubulin, forms a ring-like structure, the “Z ring,” at midcell and serves as a scaffold for divisome assembly and potential force generator during synthesis of the division septum. Both FtsA, a bacterial homolog of eukaryotic actin, and ZipA, a single-pass transmembrane protein, anchor the Z ring to the inner membrane, are required for the localization of other divisome proteins to midcell, and likely influence the assembly state of FtsZ. Positioning of the Z ring at midcell must be precise in order to ensure efficient cell division, and the MinCDE proteins have an important role in restricting the Z ring to midcell. I found that an artificial fusion of the C-terminus of MinC with MinD, instead of inhibiting Z ring formation as expected, restricted FtsA localization to only part of an intact Z ring. This resulted in many cells with division septa mostly on the side where FtsA localized, causing jackknifing of dividing cells and supporting the importance of a symmetrical FtsA ring for normal cell division. I then investigated localization patterns for FtsZ, FtsA, and ZipA in normal cells using 3D-SIM super-resolution microscopy, which showed that they generally colocalize in puncta instead of a uniformly continuous ring. Finally, I investigated the assembly of purified FtsA and FtsA mutant proteins by electron microscopy and assessed their ability to bind membranes. These studies have refined our view of the organization of the proto-ring proteins FtsZ, FtsA, and ZipA.
bacterial cell division, proto-ring, divisome, Min system, FtsZ, FtsA, ZipA