Functional Genome Mining Reveals a Class V Lanthipeptide Containing a d‐Amino Acid Introduced by an F420H2‐Dependent Reductase

Lantibiotics are a type of ribosomally synthesized and post‐translationally modified peptides (termed lanthipeptides) with often potent antimicrobial activity. Herein, we report the discovery of a new lantibiotic, lexapeptide, using the library expression analysis system (LEXAS) approach. Lexapeptide has rare structural modifications, including N‐terminal (N,N)‐dimethyl phenylalanine, C‐terminal (2‐aminovinyl)‐3‐methyl‐cysteine, and d‐Ala. The characteristic lanthionine moiety in lexapeptide is formed by three proteins (LxmK, LxmX, and LxmY), which are distinct from enzymes known to be involved in lanthipeptide biosynthesis. Furthermore, a novel F420H2‐dependent reductase (LxmJ) from the lexapeptide biosynthetic gene cluster (BGC) is identified to catalyze the reduction of dehydroalanine to install d‐Ala. Our findings suggest that lexapeptide is the founding member of a new class of lanthipeptides that we designate as class V. We also identified further class V lanthipeptide BGCs in actinomycetes and cyanobacteria genomes, implying that other class V lantibiotics await discovery. Lexapeptide is a lantibiotic showing potent antibacterial activity against Gram‐positive bacteria such as MRSA and MRSE, featured by the lanthionine (Lan) and d‐Ala formation in its structure. The formation of Lan is catalyzed by a class V lanthionine synthetase comprised of three standalone proteins. The d‐Ala28 is installed by the F420H2‐dependent reductase LxmJC, which can introduce d‐stereocenters into lanthipeptides.