Lantibiotics are post-translationally modified
peptide antimicrobial agents that are synthesized with an N-terminal leader sequence and a C-terminal propeptide. Their maturation involves enzymatic
dehydration of Ser and Thr residues in the precursor
peptide to generate unsaturated
amino acids, which react intramolecularly with nearby cysteines to form cyclic
thioethers termed lanthionines and methyllanthionines. The role of the
leader peptide in
lantibiotic biosynthesis has been subject to much speculation. In this study, mutations of conserved residues in the leader sequence of the precursor
peptide for
lacticin 481 (LctA) did not inhibit
dehydration and cyclization by
lacticin 481 synthetase (LctM) showing that not one specific residue is essential for these transformations. These
amino acids may therefore be conserved in the leader sequence of class II
lantibiotics to direct other biosynthetic events, such as proteolysis of the
leader peptide or transport of the active compound outside the cell. However, introduction of Pro residues into the
leader peptide strongly affected the efficiency of
dehydration, consistent with recognition of the secondary structure of the
leader peptide by the
synthetase. Furthermore, the presence of a hydrophobic residue at the position of Leu-7 appears important for enzymatic processing. Based on the data in this work and previous studies, a model for the interaction of LctM with LctA is proposed. The current study also showcases the ability to prepare other
lantibiotics in the class II
lacticin 481 family, including
nukacin ISK-1,
mutacin II, and
ruminococcin A using the
lacticin 481 synthetase. Surprisingly, a conserved Glu located in a ring that appears conserved in many class II
lantibiotics, including those not belonging to the
lacticin 481 subgroup, is not essential for antimicrobial activity of
lacticin 481.