Kit Pogliano
e-mail: kpogliano@ucsd.edu |
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Bacillus subtilis is a bacterium with a simple developmental pathway leading to spore formation under conditions of nutrient limitation. Shortly after the formation of the two cells required for spore formation, the membrane of the larger mother cell begins to migrate around the smaller forespore in a phagocytosis-like process known as engulfment. Ultimately the migrating membrane meets and fuses, releasing the forespore into the mother cell cytoplasm (see Figure 1). My lab seeks to understand the mechanism of engulfment, as a model system for understanding how bacteria move macromolecules within their cells. We have developed methods for the study of engulfment that are also ideal for the study of cellular polarity and protein localization. Our research is focused on three main questions:
What is the mechanism of engulfment? We have identified proteins found in all endospore forming bacteria that are required for membrane migration, and found that one of these proteins is a cell wall hydrolase. We propose that the bacterial cell wall plays a role analogous to that of the actin and tubulin network of eukaryotic cells, providing a scaffold along which proteins can move.
How do bacteria catalyze membrane fusion? The final step of engulfment is a membrane fusion event on the distal side of the forespore. We have developed an in vivo assay for this membrane fusion event, and identified a conserved bacterial protein required for membrane fusion. This protein, SpoIIIE, is also an ATP-dependent DNA translocase required for the completion of chromosome segregation into the forespore at an early stage of sporulation.
How are proteins localized within
bacterial cells? Subcellular protein targeting is an essential
feature of bacterial cells, as it is required for cell division,
chromosome segregation, as well as for development. However, in
contrast to eukaryotic cells, virtually nothing is known about the
mechanism by which bacterial proteins reach their correct subcellular
address. We are studying the mechanism by which membrane proteins
(such as the engulfment proteins) are localized to specific regions
of the cytoplasmic membrane. We are also investigating the mechanism
by which the assembly of the SpoIIIE DNA translocase is restricted
to one side of the septum, a process which establishes the polarity
of DNA segregation.
Figure 2: Dynamic localization of the SpoIIIQ (green-yellow), a protein involved in engulfment and cell-specific gene expression.
Broder, D. and K. Pogliano. (2006). Forespore engulfment mediated by a ratchet-like mechanism. Cell, 126:917-928.
Liu, N.-J. L., R.A. Dutton and K. Pogliano. (2006). Evidence that the SpoIIIE DNA translocase participates in membrane fusion during cytokinesis and engulfment. Molecular Microbiology, 59:1097-1113.
Jiang, X., A. Rubio, S. Chiba and K. Pogliano. (2005). Engulfment-regulated proteolysis of SpoIIQ: evidence that dual checkpoints control sigmaK activity. Molecular Microbiology, 58:102-115.
Blaylock, B., X. Jiang, A. Rubio, C.P. Moran, Jr. and K. Pogliano. (2004). Zipper-like interaction between proteins in adjacent daughter cells mediates protein localization. Genes & Development, 18:2916-2928.
Rubio, A. and K. Pogliano. (2004). Septal localization of forespore membrane proteins during engulfment in Bacillus subtilis. EMBO J., 23:1636-1646.
Sharp, M.D. and K. Pogliano. (2002). Role of cell-specific assembly of SpoIIIE in polarity of DNA transfer. Science, 295:137-139.
Kit Pogliano received her Ph.D. from the Department of Microbiology and Molecular Genetics at Harvard Medical School and was a Damon Runyon-Walter Winchell postdoctoral fellow at Harvard University. She is a recipient of the Searle Scholar and Beckman Young Investigator awards.
