Expanding the Structural Diversity of Drimentines by Exploring the Promiscuity of Two N-methyltransferases

Methylation is envisioned as a promising way to rationally improve key pharmacokinetic characteristics of lead compounds. Although diverse tailoring enzymes are found to be clustered with cyclodipeptide synthases (CDPSs) to perform further modification reactions on the diketopiperazine (DKP) rings generating complex DKP-containing compounds, so far, a limited number of methyltransferases (MTs) co-occurring with CDPS have been experimentally characterized. Herein, we deciphered the methylation steps during drimentines (DMTs) biosynthesis with identification and characterization of DmtMT2-1 (from Streptomyces sp. NRRL F-5123) and DmtMT1 (from Streptomyces youssoufiensis OUC6819). DmtMT2-1 catalyzes N4-methylation of both pre-DMTs and DMTs; conversely, DmtMT1 recognizes the DKP rings, functioning before the assembly of the terpene moiety. Notably, both MTs display broad substrate promiscuity. Their combinatorial expression with the dmt1 genes in different Streptomyces strains successfully generated eight unnatural DMT analogs. Our results enriched the MT tool-box, setting the stage for exploring the structural diversity of DKP derivatives for drug development.