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
2002 Fulbright Scholar Research Award
1993 Pew Scholar in Biomedical Sciences
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.
Improved X-ray diffraction from Bacillus megaterium penicillin G acylase crystals through long cryosoaking dehydration.
Rojviriya C, Pratumrat T, Saper MA, Yuvaniyama J.
Acta Crystallogr Sect F Struct Biol Cryst Commun. 2011; 67: 1570-4.
The crystal structure of Escherichia coli group 4 capsule protein GfcC reveals a domain organization resembling that of Wza.
Sathiyamoorthy K, Mills E, Franzmann TM, Rosenshine I, Saper MA.
Biochemistry. 2011; 50: 5465-76.
For a list of publications from PubMed, click HERE