Faculty

Mark A. Saper

Associate Professor of Biological Chemistry Associate Research Scientist, Biophysics Research Division

Ph.D., Rice University
Postdoctoral Fellow, Weizmann Institute & Harvard University

Research Focus: Molecular Mechanisms of Bacterial Pathogenesis

Phone: 734.764.3353
E-mail: saper@umich.edu
Fax: 734.764.3323

Our lab is keen on understanding the structure and function of two molecular machines on the surface of pathogenic Gram-negative bacteria. Specifically, we are interested in how outer membrane lipoproteins control peptidoglycan (PG) synthesis in pathogenic bacteria. We also are studying how enteropathogenic bacteria produce and secrete a high molecular weight polysaccharide to form a protective capsule that is important for causing disease. Tools of biochemistry, microbiology, and X-ray crystallography are combined to provide excellent research projects for students with varying interests.

LpoA is an outer membrane lipoprotein conserved in many Gram-negative bacteria that was recently shown to facilitate cross-linking of PG by the bifunctional PG synthase PBP1A in E. coli. This protein is essential for the growth of Haemophilus influenza, a respiratory pathogen found in children’s ear infections and patients with COPD. Although not required for growth in Proteus mirabilis in rich media, the LpoA ortholog appears essential for colonization of the bladder and kidney in severe urinary tract infections. Our crystal structures of the H. influenzae LpoA show it to be a novel fusion of a helical domain with a periplasmic-like binding protein. We are in the process of identifying the binding partners of this protein for co-crystallization experiments and to screen for antimicrobial inhibitors. We are also interested in characterizing the lpoA deletion strain of Proteus mirabilis, a pathogen responsible for hospital-acquired urinary tract infections. Although this mutant grows in lab culture, evidence from Prof. Harry Mobley’s lab (Dept of Microbiology & Immunology) suggests that is relatively avirulent in vivo. We will test the mutant in vitro and with a mouse infection assay in vivo. The crystal structure will be determined to identify structural features necessary for function.

Many pathogenic bacteria have an outer membrane polysaccharide capsule important for protection from the host immune system, attachment to host cells, and formation of biofilms. Enteropathogenic E. coli (EPEC) causes severe diarrhea and expresses a capsule comprised of O-antigen oligosaccharide repeats. The gfc operon encodes 7 genes important for capsule export. GfcD is predicted to form a large outer membrane β-barrel possibly involved in the secretion process or in anchoring the capsule to the outer membrane. We are purifying this protein and have obtained some promising crystals. Preliminary observations suggest that this protein may regulate production of the polysaccharide. Potential projects include following up on this hypothesis as well as identifying proteins that interact with GfcD. Another gfc protein is Etp, a cytoplasmic tyrosine phosphatase that is essential for capsule production. We recently published the observation that Etp is itself tyrosine phosphorylated and now would like to identify its kinase and determine if this is a new signaling pathway controlling capsule expression.

Recent publications:
Nadler, C., Koby, S., Peleg, A., Johnson, A. C., Suddala, K. C., Sathiyamoorthy, K., Smith, B. E., Saper, M. A. & Rosenshine, I. (2012). Cycling of Etk and Etp phosphorylation states is involved in formation of group 4 capsule by Escherichia coli. PLoS ONE 7, e37984. PMC336699

Sathiyamoorthy, K., Mills, E., Franzmann, T. M., Rosenshine, I. & Saper, M. A. (2011). The Crystal Structure of Escherichia coli Group 4 Capsule Protein GfcC Reveals a Domain Organization Resembling That of Wza. Biochemistry 50, 5465–5476. doi:10.1021/bi101869h

Saper Research Group

 

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.

 

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