Mapping the biosynthetic pathway of a hybrid polyketide-nonribosomal peptide in a metazoan

Hybrid polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) systems typically use complex protein-protein interactions to facilitate direct transfer of intermediates between megasynthases. In the nematode Caenorhabditis elegans, PKS-1 and NRPS-1 produce the nemamides, the only known hybrid polyketide-nonribosomal peptides in animals, through a poorly understood mechanism. Here, we use genome editing and mass spectrometry to map the roles of individual PKS-1 and NRPS-1 enzymatic domains in nemamide biosynthesis. Furthermore, we show that nemamide biosynthesis requires at least five additional stand-alone enzymes that are encoded by genes distributed across the worm genome. We identify the roles of these enzymes in the biosynthetic pathway and discover a novel mechanism of trafficking intermediates between a PKS and an NRPS. Specifically, we show that the enzyme PKAL-1 activates an advanced polyketide intermediate as an adenylate and directly loads it onto a carrier protein in NRPS-1. This trafficking provides a means by which a PKS-NRPS system can expand its biosynthetic potential and is likely important for the regulation of nemamide biosynthesis.