S224 Presents a Catalytic Trade-off in PLP-Dependent l-Lanthionine Synthase from .

Lanthionine synthase from the oral bacterium is a fold type II pyridoxal-5'-phosphate (PLP)-dependent enzyme that catalyzes the β-replacement of l-cysteine by a second molecule of l-cysteine to form HS and l-lanthionine. The -isomer of the latter product is incorporated into the peptidoglycan layer. Herein, we investigated the catalytic role of S224, which engages in hydrogen-bond contact with the terminal carboxylate of l-lanthionine in the closed conformation of the enzyme.