Fig. 1. (A) General pathway to (methyl)lanthionine formation in lanthipeptides. (B) Ring patterns of the seven peptides examined in this work. Cys residues are colored in blue, former Ser/Thr residues are colored in red, dehydroamino acids are colored in purple. Each thioether ring is marked with a letter A–D. The stereochemistry of the (Me)Lan structures of Pcn 1.1, Pcn 2.8, Pcn 2.11, and the cytolysins S and L has been experimentally determined.^32,34 The stereochemistry for Pcn 2.1 and Pcn 2.10 is inferred based on the stereochemistry determined for seven other prochlorosins.³⁴ Abu, 2-aminobutyric acid. (C) Formation of (methyl)lanthionine with different stereochemistry from precursors with a S/T-S/T-X-X-C motif.