Biosynthetic Gene Cluster of linaridin Peptides Contain Epimerase Gene

Salinipeptins belong to the type-A linaridin class of ribosomally synthesized and post-translationally modified peptides (RiPPs) comprising 22 amino acid residues with multiple D-amino acids. Although chirality of other type-A linaridins, such as grisemycin and cypemycin, has not been reported, the biosynthetic gene clusters of type-A linaridins have identical gene organization. Here, we report heterologous expression of grisemycin biosynthetic gene cluster ( grm ) and show that grisemycin contained multiple D-amino acids, similar to salinipeptins. The heterologous expression experiments also confirmed involvement of a novel peptide epimerase in grisemycin biosynthesis. Gene-deletion experiments indicated that grmL , a sole gene with unknown function, was indispensable for grisemycin production. We also show that the presence of D-amino acids is likely a common feature of linaridin natural products by analyzing two other type-A linaridin clusters.