Structure Elucidation and Activity of Kolossin A, the D-/L-Pentadecapeptide Product of a Giant Nonribosomal Peptide Synthetase

The largest continuous bacterial nonribosomal peptide synthetase discovered so far is described. It consists of 15 consecutive modules arising from an uninterrupted, fully functional gene in the entomopathogenic bacterium Photorhabdus luminescens. The identification of its cryptic biosynthesis product was achieved by using a combination of genome analysis, promoter exchange, isotopic labeling experiments, and total synthesis of a focused collection of peptide candidates. Although it belongs to the growing class of D‐/ L‐peptide natural products, the encoded metabolite kolossin A was found to be largely devoid of antibiotic activity and is likely involved in interspecies communication. A stereoisomer of this peculiar natural product displayed high activity against Trypanosoma brucei rhodesiense, a recalcitrant parasite that causes the deadly disease African sleeping sickness. Sleeping giant: A 1.8 MDa nonribosomal peptide synthetase (NRPS) was identified in the entomopathogenic bacterium Photorhabdus luminescens and its production was activated. Its 15‐mer D‐/ L‐peptide product kolossin A was structurally characterized by combining genomic analysis of the silent gene cluster, molecular biology, LC–MS, and total synthesis. A stereoisomer of kolossin A was found to be active against the pathogen that causes African sleeping sickness.