Mark A. Saper

Associate Professor of Biological Chemistry

Associate Research Scientist, Biophysics Research Division

Ph.D., Rice University

Email:  saper@umich.edu

Structural Microbiology: Mechanisms of Bacterial Pathogenicity

Pathogenic bacteria have evolved numerous molecular mechanisms for growth in often hostile environments. Our laboratory is using protein structure determination and other biochemical techniques to understand the function of several of these systems.

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 other bacterial pathogens. One domain of the protein resembles proteins involved in bacterial small molecule transport. Together with Brian Akerley (U. Mass) we are taking both a genetic and structural approach to determinng the protein's function and its suitability as an antigen for vaccine development or as a drug target. Structures of both domains are being determined and the search for a potential ligand is in progress. We also are characterizing its location, expression and partner proteins in the bacteria itself.

Many bacteria have an outer membrane polysaccharide capsule that aids in bacterial attachment to host cells, formation of biofilms, and protection from the immune system. How are these oligosaccharides synthesized and transported to the exterior of the cell? 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 essential for capsule production. Several of the proteins are novel and include a protein tyrosine kinase and phosphatase. Besides crystallization studies and characterization of enzyme kinetics, we seek to understand the molecular mechanism of how the essential autophosphorylation of the kinase controls the polymerizaon of the polysaccharide. See Peleg et al. (2005) below for more information.

Besides employing state-of-the-art techniques in crystal structure determination, students in the lab will develop protein expression systems, learn protein purification techniques, and measure molecular interactions by calorimetry and spectroscopy (including fluorescence). Excellent opportunities exist for motivated undergraduates as well as graduate students and postdoctoral fellows.

The Saper Lab is affiliated with these graduate programs:

• Program in Biomedical Sciences (Biological Chemistry & Biophysics)
• Biophysics Graduate Program
• Molecular Biophysics Training Program
• Chemical Biology Graduate Program

Representative Publications

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. (2005). Identification of an Escherichia coli operon required for formation of the O-antigen capsule. J Bacteriol,187(15), 5259–5266.

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 cooperate to promote bacterial virulence. Mol. Microbiol. 55: 1346–1356.

Khandelwal, P., Keliikuli, K., Smith, C. L., Saper, M.A. & Zuiderweg, E.R.P. (2002). Solution structure and phosphopeptide binding to the N-terminal domain of Yersinia YopH. Biochemistry 41(38):11425–11437.

Smith, C.L., Khandelwal, P., Keliikuli, K., Zuiderweg, E.R.P. & Saper, M.A. (2001). Structure of the Type III Secretion and Substrate-Binding Domain of the Yersinia YopH Phosphatase. Mol. Microbiol. 42, 967–979.

Vijayalakshmi, J., Mukhergee, M. K., Graumann, J., Jakob, U. & 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.

Postal Address:

Mark A. Saper, Ph.D.
Biophysics Research Division
930 North University Ave
Ann Arbor MI 48109-1055
U.S.A.

Below: Noncatalytic substrate-binding site important for localization of YopH to host substrate. See Ivanov et al. (2005).