Hrvatsko genetièko društvo (grupa za molekularnu biologiju) i Zavod za molekularnu biologiju Instituta “Ruðer Boškoviæ”

pozivaju Vas na zajednièki kolokvij

petak, 23. studenog 2007. godine u 14.00 sati
dvorana III krila, Institut “Ruðer Boškoviæ”, Bijenièka 54, Zagreb

Prof. dr. sc. Igor Štagljar
Terrence Donnelly Centre for Cellular and Biomolecular Research (CCBR)
Department of Biochemistry & Department of Molecular Genetics
University of Toronto, Toronto, Canada

Yeast as a test-tube for drug discovery: lessons from the opportunistic human pathogen Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that is a key factor in the mortality of cystic fibrosis patients, and infection represents an increased threat for human health worldwide. Because resistance of Pseudomonas aeruginosa to antibiotics is increasing, new inhibitors of pharmacologically validated targets of this bacterium are needed. Here we demonstrate that a cell-based yeast phenotypic assay, combined with large-scale inhibitor screen, identified small molecule inhibitors that can relieve the toxicity caused by heterologous expression of selected Pseudomonas aeruginosa Open Reading Frames (ORFs). We identified the first small molecule inhibitor of Exoenzyme S (ExoS), a toxin involved in Type III secretion. We show that this inhibitor, exosin, modulates ExoS ADP-ribosyltransferase activity in vitro suggesting the inhibition is direct. Moreover, exosin and two of its derivatives display a significant protective effect against Pseudomonas infection in vivo. Furthermore, because the assay was performed in yeast, we were able to demonstrate that several yeast homologs of the known human ExoS targets are likely ADP-ribosylated by the toxin. For example, using an in vitro enzymatic assay, we demonstrate that yeast Ras2p is directly modified by ExoS. Lastly, by surveying a collection of yeast deletion mutants, we identified Bmh1p, a yeast homologue of the human FAS, as an ExoS cofactor, revealing a partial conservation of the bacterial toxin mode of action in both yeast and human. Taken together, our integrated cell-based, chemical-genetic approach demonstrates that such screens can augment traditional drug screening approaches and can facilitate the discovery of new compounds against a broad range of human pathogens.
Reference:
Arnoldo, A., Curak, J., Kittanakom, S., Chevelev, I., Lee, V.T., Sahebol-Amri, M., Koscick, B., Ljuma, L., Roy, P.J., Bedalov, A., Nislow, A. Merrill, R., C., Lory, S., and Stagljar, I. (2007) Isolating small molecule inhibitors of Pseudomonas aeruginosa ExoS toxin using a yeast phenotypic screen, PLoS Genetics, in press.

Predsjednica HGD-a:
Prof.dr.sc. Jasna Franekiæ, PBF

Koordinatori predavanja:
Dr. sc. Ksenija Zahradka, zn. sur., IRB
Dr. sc. Krešimir Gjuraèiæ, GSK Research Centre Zagreb Ltd.