Mark Saper, Ph.D.

Associate Professor, Biological Chemistry
Associate Research Scientist, Biophysics

Ofc: 3220B MSRB III

Lab: 3323 MSRB III

1150 W. Medical Center Drive

Ann Arbor, MI  48109-5606

 

(734) 764-3353

Areas of Interest

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 polysaccharide. We collaborate with Prof. Ilan Rosenshine (Hebrew University), whose lab 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 capsule 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 group 4 capsule 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.

Honors & Awards

Fulbright Scholar Research Award, 2002
Pew Scholar in Biomedical Sciences, 1993

Published Articles or Reviews

Recent Publications

Structural basis of peptidoglycan endopeptidase regulation.
Shin JH, Sulpizio AG, Kelley A, Alvarez L, Murphy SG, Fan L, Cava F, Mao Y, Saper MA, Dörr T.
Proc Natl Acad Sci U S A. 2020; 117: 11692–702.

Structure of the capsule and lipopolysaccharide O-antigen from the channel catfish pathogen, Aeromonas hydrophila.
Heiss C, Wang Z, Thurlow CM, Hossain MJ, Sun D, Liles MR, Saper MA, Azadi P.
Carbohydr Res. 2019; 486: 107858.

Crystal Structure Of Photorespiratory Alanine:Glyoxylate Aminotransferase 1 (AGT1) From Arabidopsis thaliana.
Liepman AH, Vijayalakshmi J, Peisach D, Hulsebus B, Olsen LJ, Saper MA.
Front Plant Sci. 2019; 10: 1229.

Crystal structures of the amino-terminal domain of LpoA from Escherichia coli and Haemophilus influenzae.
Kelley A, Vijayalakshmi J, Saper MA.
Acta Crystallogr F Struct Biol Commun. 2019; 75: 368–76.

Structural analyses of the Haemophilus influenzae peptidoglycan synthase activator LpoA suggest multiple conformations in solution.
Sathiyamoorthy K, Vijayalakshmi J, Tirupati B, Fan L, Saper MA.
J Biol Chem. 2017; 292: 17626–42.

Cycling of Etk and Etp phosphorylation states is involved in formation of group 4 capsule by Escherichia coli.
Nadler C, Koby S, Peleg A, Johnson AC, Suddala KC, Sathiyamoorthy K, Smith BE, Saper MA, Rosenshine I.
PLoS One. 2012; 7: e37984.

For a list of publications from PubMed, click HERE