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.