Heterologous Production and Bioactivity Investigation of the Potential Medicinal Lantibiotic Actagardine

Lantibiotics are a class of ribosomally synthesized and post-translational modified antimicrobial peptides, which contain lanthionine or methylanthionine rings. During post-translational modifications, serine and theorine residues in lantibiotic precursor peptides are normally dehydrated and attacked by cysteine residues via intramolecular Michael addition, catalyzed by modification enzymes. This formation of rings gives the lantibiotics a more rigid conformation that possesses higher resistance to proteolytic degradation. Actagardine is a globular lantibiotic, which is stable in simulated gastric fluid and possesses highly potent antimicrobial activity against Clostridium difficile, a gram-positive bacteria prone to cause severe diarrhea after treatments of regular antibiotics. One derivative of actagardine, NVB302 has already entered clinical trials for treating C. difficile. Currently actagardine and its derivatives are produced by fermentation with the introduction of the whole actagardine biosynthesis cluster. We have shown that the production of actagardine and its derivatives can be simplified by coexpression in E. coli, confirming the possibility of heterologous biosynthesis of potent antibiotics with multiple post-translational modifications using the E. coli co-expression system.  Actagardine is also the only known lantibiotic bearing a sulfoxide group. We investigated the monooxygenase (GarO) in the actagardine biosynthesis cluster for its in vivo and in vitro activity catalyzing the formation of the sulfoxide group, expanding current knowledge of lantibiotic biosynthesis enzymes.