gramicidin S biosynthesis gramicidin biosynthesis PMID:15938641 pathway GO:1901103 Biosynthesis of gramicidin S antibiotic. The linear pentadecapeptide gramicidin has been reported to be assembled by four large multimodular nonribosomal peptide synthetases (NRPSs), LgrABCD, that comprise 16 modules. During biosynthesis, the N-formylated 16mer peptide is bound to the peptidyl carrier protein (PCP) of the terminal module via a thioester bond to the carboxyl group of the last amino-acid glycine(16). In a first reaction the peptide is released from the protein template in an NAD(P)H-dependent reduction step catalyzed by the adjacent reductase forming an aldehyde intermediate. This aldehyde intermediate is further reduced by an aldoreductase, LgrE, in an NADPH-dependent manner to form the final product gramicidin A, N -formyl-pentadecapeptide-ethanolamine. UPa:UPA00102 antibiotic biosynthesis