Angewandte Chemie | 2021
Structural and functional analyses of the tridomain-nonribosomal peptide synthetase FmoA3 for 4-methyloxazoline ring formation.
Abstract
Nonribosomal peptide synthetases (NRPSs) are attractive targets for bioengineering to generate useful peptides . F moA3 is a single modular NRPS composed of heterocyclization (Cy), adenylation (A), and peptidyl carrier protein (PCP) domains. It use s 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 activit y. The collective data support a proposed catalytic cycle of FmoA3.