Molecular Basis of Ligand Recognition by the Taurine/Amino Acid Chemoreceptor of Vibrio cholerae

Abstract

Vibrio cholerae, an etiological agent of cholera, is attracted by various amino acids and taurine, a component of bile. A chemoreceptor homolog (Mlp37) was found to mediate taxis to both taurine and amino acids. Direct binding of taurine and amino acids to the periplasmic fragment of Mlp37 was observed by isothermal titration calorimetry. Ligand-occupied structures of the Mlp37 fragment revealed that the ligand-binding pocket has an opening, large enough to accommodate a larger side chain, and contains several common residues that can interact with taurine and different amino acids without substantial displacements. This structural information allowed us to visualize ligand binding to Mlp37 with fluorescently labeled serine.