Date of Graduation

5-2014

Document Type

Dissertation (PhD)

Program Affiliation

Microbiology and Molecular Genetics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

William Margolin, Ph.D.

Committee Member

Peter Christie, Ph.D.

Committee Member

Carmen Dessauer, Ph.D.

Committee Member

Michael Lorenz, Ph.D.

Committee Member

Kevin Morano, Ph.D.

Abstract

Division of a bacterial cell into two equal daughter cells requires precise assembly and constriction of the division machinery, or divisome. The Escherichia coli divisome includes nearly a dozen essential cell division proteins that assemble at midcell between segregating sister chromosomes. FtsZ, a homolog of eukaryotic tubulin, is the first essential cell division protein to localize at midcell where it polymerizes into a ring-shaped scaffold (Z ring). Establishment of the Z ring is required for recruitment of downstream cell division proteins including FtsA, a cytoplasmic protein that tethers the Z ring to the inner membrane. Following localization of FtsA and other early cell division proteins, a number of additional cell division proteins are recruited to midcell. The last essential cell division protein to be recruited to the divisome is FtsN, a transmembrane protein with a small cytoplasmic tail and a large periplasmic domain. Although the temporal order of divisome assembly is well established, the essential functions of the majority of the divisome proteins are not known. Additionally, many interactions among the cell division proteins have been suggested using in vivo assays, but few have been demonstrated biochemically. Identifying these functions and interactions is vital to understanding the mechanisms that drive bacterial cell division.

Although FtsA localizes to division sites early, previous data suggested that FtsA interacts with the late cell division protein FtsN. To confirm the FtsA-FtsN interaction observed in vivo, protein-protein interaction assays were performed in vitro. These assays showed that the interaction between FtsA and FtsN was direct, and that the cytoplasmic and transmembrane domains of FtsN (FtsNCyto-TM) were sufficient for interaction with FtsA. Suprisingly, FtsNCyto-TM localized to midcell in an FtsA-dependent manner, independent of FtsN’s periplasmic localization domain (SPOR). I discovered that both the cytoplasmic and SPOR domains facilitate midcell localization of FtsN and that loss of both domains abolishes recruitment to the divisome. These results suggest that one role of FtsA-FtsN interaction is to localize FtsN more efficiently to midcell. Together, these data provide a better understanding of how and why E. coli cell division proteins interact to ensure faithful and robust operation of the divisome.

Keywords

Cell division, FtsA, FtsN, FtsZ, SPOR