Faculty

Pathogenic bacteria have evolved molecular mechanisms for growth and evasion of host immune systems. Our laboratory is using protein structure determination by X-ray crystallography combined with other biochemical techniques to understand the function of these proteins.

Some animal and plant bacterial pathogens inject virulence proteins (effectors) directly into the cytoplasm of infected host cells through a Type III Secretion System (TTSS). These proteins disrupt normal cell signaling and prevent the host from mounting an effective immune response. We are particularly interested in how the effectors are recognized by the TTSS injectosome, an elaborate needle structure powered by an ATP-dependent motor. Unlike other effectors, nine effectors from Salmonella have a conserved amino-terminal domain essential for secretion into the host cell. We have just determined the crystal structure of one of these domains. Future work will identify what parts of this domain are important for secretion and how this domain interacts with the injectosome. Additionally, we are examining how this domain binds to host cell proteins to target the effector to specific organelles.

Haemophilus influenzae is the primary cause of ear infections in children and lung infections of chronically ill smokers. Recently, many genes have been identified that are essential for growth of Haemophilus but have unknown function. One of these, YraM, is a two-domain lipoprotein also found in several bacterial pathogens. We are taking both a genetic and structural approach to determine the protein's function and test its suitability as a drug target an antigen for vaccine development or.

Many bacteria have an outer membrane polysaccharide capsule recognized by the host's immune system that also aids in bacterial attachment to host cells and formation of biofilms. How are these oligosaccharides synthesized and transported to the exterior of the cell? Is the capsule essential for bacterial virulence? Recently, in collaboration with Dr. Ilan Rosenshine, Hebrew University Faculty of Medicine, we have discovered a new operon of 7 genes in enteropathogenic E. coli that are necessary for capsule production. Several of the proteins are novel and include a tyrosine kinase and phosphatase. Enzyme kinetics and structural studies are in progress.

Awards

Pew Scholar in the Biomedical Sciences
Fulbright Research Fellow
Lady Davis Scholarship

Representative Publications

1. Peleg, A., Shifrin, Y., Ilan, O., Nadler-Yona, C., Nov, S., Kobi, S., Baruch, K., Altuvia, S., Elgrably-Weiss, M., Abe, C., Knutton, S., Saper, M.A. and Rosenshine, I., "Identification of an Escherichia coli operon required for formation of the O-antigen capsule", J. Bacteriol., 2005, in press.

2. Ivanov, M.I., Stuckey, J.A., Schubert, H.L., Saper, M.A. and Bliska, J.B., "Two Novel Substrate Targeting Sites in the Yersinia Protein Tyrosine Phosphatase Cooperate to Promote Bacterial Virulence", Mol. Microbiol., 2005, 55, 1346-1356.

3. Khandelwal, P., Keliikuli, K., Smith, C.L., Saper, M.A. and Zuiderweg, E.R., "Solution Structure and Phosphopeptide Binding to the N-terminal Domain of Yersinia YopH: Comparison with a Crystal Structure", Biochemistry, 2002, 41, 11425.

4. Smith, C.L., Khandelwal, P., Keliikuli, K., Zuiderweg, E.R.P. and Saper, M.A., "Structure of the Type III Secretion and Substrate-binding Domain of Yersinia YopH Phosphatase", Mol. Microbiol., 2001, 42, 967.

5. Vijayalakshmi, J., Mukhergee, M.K., Graumann, J., Jakob, U. and Saper, M.A., "The 2.2 Å Crystal Structure of Hsp33: A Heat Shock Protein with Redox-regulated Chaperone Activity", Structure, 2001, 9, 367.