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 contains multiple D-amino acids, similar to salinipeptins. The heterologous expression experiments also confirm the involvement of a novel peptide epimerase in grisemycin biosynthesis. Gene-deletion experiments indicate that grmL, a single gene with unknown function, is 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.
Keywords: D-amino acids; biosynthesis; epimerases; linaridin; peptides.
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