Deciphering the Enzymatic Function of the Bovine Enteric Infection Related Protein YfeJ from Salmonella enterica Serotype Typhimurium.

Non-typhoidal Salmonella can colonize the gastro-intestinal system of cattle and can also cause significant food-borne disease in humans. The use of a library of single-gene deletions in Salmonella enterica serotype Typhimurium allowed identification of several proteins that are under selection in the intestine of cattle. STM2437 (yfeJ) encodes one of these proteins, and it is currently annotated as a type I glutamine amidotransferase. STM2437 was purified to homogeneity, and its catalytic properties with a wide range of gamma-glutamyl derivatives were determined. The catalytic efficiency toward the hydrolysis of L-glutamine was extremely weak with a k(cat) /K-m value of 20 M(-1)s(-1) gamma-L-Glutamyl hydroxamate was identified as the best substrate for STM2437, with a k(cat) /K-m value of 9.6 X 10 (4) M-1 s(-1). A homology model of STM2437 was constructed on the basis of the known crystal structure of a protein of unknown function (Protein Data Bank entry 3L7N), and gamma-L-glutamyl hydroxamate was docked into the active site based on the binding of L-glutamine in the active site of carbamoyl phosphate synthetase. Acivicin was shown to inactivate the enzyme by reaction with the active site cysteine residue and the subsequent loss of HCl. Mutation of Cys91 to serine completely abolished catalytic activity. Inactivation of STM2437 did not affect the ability of this strain to colonize mice, but it inhibited the growth of S. enterica Typhimurium in bacteriologic media containing gamma-L-glutamyl hydroxamate.