FIG. 7.

Model of the nodularin biosynthetic pathway catalyzed by proteins encoded by ndaC to -F. The squares represent the NRPS adenylation (A), peptidyl carrier protein (PCP), and condensation (C) domains. The circles represent the PKS, ketosynthase (KS), acyltransferase (AT), C-methyltransferase (CM), dehydratase (DH), ketoreductase (KR), and acyl carrier protein (ACP) domains. Condensation reactions are indicated in red. The O-methyltransferase (OM) NdaE catalyzes the transfer of the methyl group to the C₉ hydroxyl. The racemase NdaG catalyzes the epimerization of the Glu residue. The aminotransferase (AMT) domain catalyzes the transfer of the amine group to Adda. Peptide condensation reactions are catalyzed by NdaA and NdaB. The putative dehydrogenase, NdaH, catalyzes the formation of the MeDhb residue following peptide bond formation. The thioesterase (TE) domain catalyzes the cyclization and release of the peptide.