& Molecular Biology
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Department of Biochemistry & Molecular Biology |
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Home Faculty Secondary Faculty Awad. W. Barredo, Barrientos, T. Baumbach, L. Carraway, K. Elsas, L. Howard, G. Hu, Jennifer King, M.L. Neary, J. Norenberg, M. Schesser, K. Schiller, P. Slingerland, J. Primary Faculty Staff Graduate Program Undergraduate Program Medical Program DNA Core Lab Journal Club Evaluations Calendar |
 Kurt
Schesser
Associate Professor of
Microbiology and Immunology Research Interests: Multicellular life arose about a billion years ago in a world that had long been dominated by unicellular microbes. It's clear that multicellularity allowed for the evolution of an elaborate and sophisticated defense system. It is also evident that the microbes, at least many of the ones we recognize today as pathogens, were not standing idle during the last three billion years. Far from being a ‘bag of enzymes’, the bacteria have evolved elaborate and sophisticated ways of their own to mollify host defense responses. A clear example of an 'anti-immune system' can be found in many species of Gram-negative bacteria that employ a protein secretion system (designated as type III) that delivers ‘toxins’ directly into eukaryotic cells. Our lab is interested in both how the functioning of this secretion system activity is coordinated with other bacterial cellular processes as well as deciphering the activity of the toxins within the eukaryotic host cell (referred to below as ‘delivery’ and ‘cellular microbiology’, respectively). |
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The ‘Delivery’ Problem During their life-and-death struggle with the microphage, the pathogenic yersiniae (Y. pestis, Y. pseudotuberculosis, Y. enterocolitica) devote a substantial amount of their metabolism to producing the toxins described above. In fact, using culture conditions that result in maximal expression of the various components of the type III secretion system, the yersiniae halt their cellular replication and literally turn into toxin export factories. However, during an actual infection of a macrophage, the yersiniae do in fact proliferate (i.e. undergo cellular replication) in addition to employing their type III secretion systems. Our lab is interested in how these ‘survival’ and ‘proliferation’ activities are coordinated in individual bacterial cells vis-à-vis the macrophage. We have recently completed a series of experiments using quantitative fluorescent microscopy and flow cytometry to follow these activities in a genetically engineered reporter strain (Wiley et al. 2007). These studies involved measuring type III expression levels of individual bacteria in various activation states. We are now developing imaging techniques that will allow us to follow type III activity and cellular replication in real time. A separate line of research on the ‘delivery’ problem originated with our observation that the ribonuclease polynucleotide phosphorylase (PNPase) is required for the optimal functioning of the yersiniae type III secretion system (Rosenzweig et al. 2005; 2007). Quite to our surprise, this effect was independent of PNPase’s ribonuclease activity and instead was only dependent on a small region of PNPase that is involved in RNA binding (the S1 domain). Recently we have found that yet an additional ribonuclease, RNase E, is involved in regulating the type III secretion system and that RNase E and PNPase likely affect secretion through a common pathway (Yang et al. 2008). Our current challenge is determining the molecular mechanisms that link these two ribonucleases and the type III secretion system. ‘Cellular Microbiology’ Not surprisingly since they are active within eukaryotic cells, the majority of the toxins secreted by type III systems possess eukaryotic-like domains or motifs. Based on sequence and in some cases structural analysis it has been suggested that the genes encoding some of the type III toxins were in fact stolen from eukaryotic genomes. Of course an unmodified eukaryotic protein itself would likely not be of much use for a bacterium since such a protein would still be responsive to normal cellular regulatory processes. Instead, ‘captured’ genes would be expected to undergo extensive modifications that would result in them becoming beneficial to the bacterium and, conversely, detrimental to the host in which they originally evolved to serve. Therefore, these toxins we observe today likely are the products of two sequential (and opposing!) lines of evolution. We are interested in determining exactly what these toxins are doing inside eukaryotic cells. Fortunately for us, 5 of the 6 toxins expressed by the pathogenic yersiniae possess similar activities in animal and yeast cells (Wiley et al. 2006). Our basic approach is to use yeast as a model system to discover aspects of toxin biology that would be difficult (or impossible!) to find using infection- and/or transfection-based model systems. For toxins like YpkA, in which we have little idea of their cellular activity, we have performed large-scale mutagenesis screens and have isolated yeast variants that are resistant to YpkA activity. We are currently characterizing the loci conferring YpkA resistance. We are taking a more directed approach for other toxins in which we have some idea of their cellular activity. For example, YopJ blocks signaling pathways that are normally activated in vertebrate cells following contact with bacteria or exposure to bacterially-derived compounds (Schesser et al. 1998; Meijer et al. 2000). In yeast cells, we have found that YopJ is active against the homologous MAP kinase signaling pathways and are taking advantage of the vast array of genetic and biochemical tools available to study the intersection of YopJ and cellular stress responses. For both our YpkA- and YopJ-based studies, discoveries made in our yeast model are verified (or not) in cell culture and animal infection assays. Lab Members: Current Lab Members Collaborators Former Lab Members (current positions and
locations) Representative Publications Yang, J., C. Jain, and K. Schesser. 2008. RNase E
regulates the Yersinia type 3 secretion system. Journal of Bacteriology
(in press). Wiley, D. J., R. Nordfeldt, J. A. Rosenzweig, C. J. DaFonseca, R. Gustin, H. Wolf-Watz, and K. Schesser. 2006. The Ser/Thr kinase activity of the Yersinia protein kinase A (YpkA) is necessary for full virulence in the mouse, mollifying phagocytes, and disrupting the eukaryotic cytoskeleton. Microbial Pathogenesis 40:234-243. Francis, M., K. Schesser, A. Forsberg, and H. Wolf-Watz. 2005. Type III secretion systems in animal-and plant-interacting bacteria. In Cellular Microbiology, 2nd edition (eds. P. Cossart, P. Boquet, S. Normark, and R. Rappuoli). ASM Press, Washington, D.C. Rosenzweig, J. A, G. Weltman, G. V. Plano, and K. Schesser. 2005. Modulation of yersinia type three secretion system by the S1 domain of polynucleotide phosphorylase. Journal of Biological Chemistry 280:156-63. Plano , G.V., M.L Niles, and K. Schesser. 2003. Type III secretion systems. In Bacterial Protein Toxins. (eds. J. Barbieri, R. Rappuoli, B. Iglewski, and D. Burns) ASM Press, Washington, D.C. Bartra, S., P. Cherepanou, A. Forsberg, and K. Schesser. 2001. The Yersinia YopE and YopH type III effector proteins enhance bacterial proliferation following contact with eukaryotic cells. BMC Microbiol. 2001;1(1):22. Schesser, K . 2001. Secretion Systems. In Encylopedia of Genetics (eds. S. Brenner and J. Miller). Academic Press. Dukuzumuremyi, J.-M., R. Rosqvist, B. Hallberg, B. Akerstrom, H. Wolf-Watz, and K. Schesser. 2000. The Yersinia protein kinase A is a host factor inducible RhoA/Rac- binding virulence factor. Journal of Biological Chemistry 275:35281-35290.
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