Mark A. Saper, Ph.D.

Associate Professor, Biological Chemistry

B.S., University of Connecticut
Ph.D., Rice University
Postdoctoral, Weizmann Institute & Harvard University

Research Profile

Human diseases caused by enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) Escherichia coli remain a major problem worldwide, especially for children in developing countries. Unlike laboratory strains, these bacteria are surrounded with a high molecular weight group 4 capsule polysaccahride. We collaborate with Prof. Ilan Rosenshine (Hebrew University Faculty of Medicine), whose lab recently demonstrated that EHEC group 4 capsule is important for bacterial virulence. Together, we identified the g4c operon encoding seven proteins, each essential for group 4 secretion (Peleg et al., 2005). Our long-term goal is a detailed molecular understanding of how reversible tyrosine phosphorylation regulates capsule biosynthesis.

Applying biochemical and structural techniques, we are focusing on two enzymes: a transmembrane protein tyrosine kinase (Etk) and a cytoplasmic low molecular weight tyrosine phosphatase (Etp). The Etk catalytic domain is structurally unrelated to eukaryotic kinases but is most similar to some bacterial ATPases. It autophosphorylates the seven tyrosines found at the C-terminus of other Etk molecules, while Etp dephosphorylates Etk. The catalytic rates of both enzymes appear to be important for proper G4C secretion. We are studying kinetics of both Etk and Etp mutants to understand the effect of the mutations on polysaccharide secretion , as well as on the activity of each other. Another project investigates why a particular Etp mutant, which is fully active in vitro and in vivo, prevents formation of the capsule. The lab is also expressing new constructs of Etk in order to obtain crystals of enzyme-substrate complexes for structure determination. Another study involves studying the size of capsule polysaccharide molecules and how they are attached to the bacteria's outer membrane.

Awards

1993 Pew Scholars Program in Biomedical Sciences
2002 Fulbright Scholar Research Award

PubMed Search Term : saper m [AU] 1972:3000 [dp]

Publications

Fauman, E.B., Cogswell, J.P., Lovejoy, B., Rocque, W.J., Holmes, W., Montana, V.G., Piwnica-Worms, H., Rink, M.J., and Saper, M.A. (1998) Crystal structure of the catalytic domain of the human cell cycle control phosphatase, Cdc25A. Cell 93: 617–625.

Smith, C.L., Khandelwal, P., Keliikuli, K., Zuiderweg, E.R.P., and Saper, M.A. (2001) Structure of the type III secretion and substrate-binding domain of Yersinia YopH phosphatase. Mol Microbiol 42: 967-979.

Vijayalakshmi, J., Mukhergee, M.K., Graumann, J., Jakob, U., and Saper, M.A. (2001) The 2.2 Å crystal structure of Hsp33: A heat shock protein with redox-regulated chaperone activity. Structure 9: 367–375. PMID: 11377197

Khandelwal, P., Keliikuli, K., Smith, C.L., Saper, M.A., and Zuiderweg, E.R. (2002) Solution Structure and Phosphopeptide Binding to the N-terminal Domain of Yersinia YopH: Comparison with a Crystal Structure. Biochemistry 41: 11425-11437. PMID: 12234185

Ivanov, M.I., Stuckey, J.A., Schubert, H.L., Saper, M.A., and Bliska, J.B. (2005) Two substrate-targeting sites in the Yersinia protein tyrosine phosphatase co-operate to promote bacterial virulence. Molecular Microbiology, Published Online: Jan 12, 2004, doi:10.1111/j.1365-2958.2005.04477.x. PMID: 15720545

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. & Rosenshine, I. (2005). Identification of an Escherichia coli operon required for formation of the O-antigen capsule. J Bacteriol 187, 5259–5266. PMID: 16030220

Vijayalakshmi, J., Akerley, B.J. & Saper, M.A. (2008). Structure of YraM, a protein essential for growth of Haemophilus influenzae. Proteins, 73(1), 204–217. PMID: 18412262