Substrate Specificity of a Methyltransferase Involved\nin the Biosynthesis of the Lantibiotic Cacaoidin

Modification of the\nN- and C-termini of peptides enhances their\nstability against degradation by exopeptidases. The biosynthetic pathways\nof many peptidic natural products feature enzymatic modification of\ntheir termini, and these enzymes may represent a valuable pool of\nbiocatalysts. The lantibiotic cacaoidin carries an <i>N</i>,<i>N</i>-dimethylated N-terminal amine group. Its biosynthetic\ngene cluster encodes the putative methyltransferase Cao4. In this\nwork, we present reconstitution of the activity of the enzyme, which\nwe termed CaoS<sub>C</sub> following standardized lanthipeptide nomenclature,\nusing a heterologously produced peptide as the model substrate. In\nvitro methylation of diverse lanthipeptides revealed the substrate\nrequirements of CaoS<sub>C</sub>. The enzyme accepts peptides of varying\nlengths and C-terminal sequences but requires dehydroalanine or dehydrobutyrine\nat the second position. CaoS<sub>C</sub>-mediated dimethylation of\nnatural lantibiotics resulted in modestly enhanced antimicrobial activity\nof the lantibiotic haloduracin compared to that of the native compound.\nImproved activity and/or metabolic stability as a result of methylation\nillustrates the potential future application of CaoS<sub>C</sub> in\nthe bioengineering of therapeutic peptides.