Biosynthesis in vitro of bacillamide intermediate-heterocyclic AlaCys by heterologous expression of nonribosomal peptide synthetase (NRPS).

Bacillamide C, a potential natural antialgae active compound, is produced by Bacillus atrophaeus C89 derived from marine sponge Dysidea avara. A nonribosomal peptide synthetase (NRPS) cluster is hypothesized to be involved in the biosynthesis of bacillamide C. The NRPS with a domain string of A1-PCP1-Cy-A2-PCP2-C can be divided into three functional modules. After heterologous expression and purification of module A1-PCP1 and module Cy-A2-PCP2, their catalytic activities were biochemically proven in vitro by the reaction with the apo-PCP domain transformed to the holo-PCP domain through a phosphopantetheinyl transferase, ATP, and substrate amino acids. Five- membered heterocyclic AlaCys with molecular weight of 172.0389 was detected. This proved the formation of the heterocyclic dipeptide AlaCys, which is considered to be a building block for the biosynthesis of bacillamide. This study provides a basis for further biosynthesis of bacillamides.