Inhibition and Structural Changes of O -Acetylserine Sulfhydrylase-A from Salmonella typhimurium Upon Binding Sulfate and Chloride Anions

Two anion binding sites, for sulfate and chloride ions, on O-acetylserine sulfhydrylase-A were determined using X-ray data. The sulfate ion binding site is similar to the carboxylate moiety of the substrate analogue methionine in the closed conformation, while the chloride ion binding site is located at the interface of the dimer. Both anions inhibit enzyme activity, but with different inhibition patterns, reflecting differences in the binding sites for the two anions.