Lantibiotics are
peptide antibiotics, realizing their unique secondary structure by posttranslational modifications, the most important one being the formation of the characteristic
amino acid lanthionine. Like other ribosomal
peptide antibiotics, they are synthesized with an N-terminal
leader peptide important for posttranslational processing by modifying
enzymes; after
peptide maturation, the
leader peptide is proteolytically cleaved off. Numerous studies of the
leader peptides of class I and II
lantibiotics already showed their crucial role in recognition, self-immunity, and extracellular transport. The recently described labyrinthopeptins, members of the family of class III
lantibiotics, exhibit the characteristic novel
amino acid labionin, which was revealed by elucidation of the structure of
labyrinthopeptin A2. The assembly of the labionin motif in the linear
peptide chain is mediated by the
lyase-
kinase-cyclase-type
enzyme LabKC through a
serine side chain phosphorylation with
GTP, elimination of the
phosphate group, and a subsequent 2-fold Michael-type addition cyclization. In this work, we systematically investigated for the first time the importance of the
leader peptide in the processing of class III
lantibiotics using the example of the
labyrinthopeptin A2 precursor
peptide. In vitro studies with synthetic
leader peptide analogues revealed that a conserved N-terminal hydrophobic patch on a putative helical structure is required for the proper
peptide processing by the modifying
enzyme LabKC. On the other hand, studies showed that the C-terminal part of the
leader peptide serves as a spacer between the binding site and active sites for phosphorylation and elimination, thus restricting the number of hydroxy
amino acid side chains that could undergo
dehydration. Finally, a model for the
peptide recognition and processing by the LabKC has been postulated.