Enzymatic synthesis of non-natural flavonoids by combining geranyl pyrophosphate C6-methyltransferase and aromatic prenyltransferase.

Terpenoids are the largest class of natural products and are derived from C5 isoprene units. Recent discoveries of modification enzymes in native isoprene units before cyclization or transfer reactions have revealed that C5 units with additional carbon atoms are also used to produce terpenoids. These reports indicate that the utilization of these modification enzymes is useful for the enzymatic production of non-natural terpenoids. In this study, we have attempted to produce methylgeranyl polyphenols, which are not observed in nature, by combining a geranyl pyrophosphate C6 methyltransferase, BezA, which was discovered from the benzastatin biosynthetic pathway, and the promiscuous prenyltransferase NphB, which catalyzes prenylation of various flavonoids. We successfully synthesized five methylgeranylated flavonoids from naringenin, apigenin, and genistein. This result demonstrates that BezA is a powerful tool for the synthesis of novel non-natural terpenoids.

Structural and Functional Analyses of the Tridomain-Nonribosomal Peptide Synthetase FmoA3 for 4-Methyloxazoline Ring Formation.

Nonribosomal peptide synthetases (NRPSs) are attractive targets for bioengineering to generate useful peptides. FmoA3 is a single modular NRPS composed of heterocyclization (Cy), adenylation (A), and peptidyl carrier protein (PCP) domains. It uses α-methyl-l-serine to synthesize a 4-methyloxazoline ring, probably with another Cy domain in the preceding module FmoA2. Here, we determined the head-to-tail homodimeric structures of FmoA3 by X-ray crystallography (apo-form, with adenylyl-imidodiphosphate and α-methyl-l-seryl-AMP) and cryogenic electron microscopy single particle analysis, and performed site-directed mutagenesis experiments. The data revealed that α-methyl-l-serine can be accommodated in the active site because of the extra space around Ala688. The Cy domains of FmoA2 and FmoA3 catalyze peptide bond formation and heterocyclization, respectively. FmoA3's Cy domain seems to lose its donor PCP binding activity. The collective data support a proposed catalytic cycle of FmoA3.