The intricate nonribosomal assembly of a potent antifungal lipopeptide from the Burkholderia cepacia complex

The Burkholderia cepacia complex (BCC) is a group of Gram-negative bacteria known for their pathogenicity to patients suffering from cystic fibrosis (CF). The BCC-belonging strain B. pyrrocinia BC11 (formerly B. cepacia BC11) produces AFC-BC11, a compound with strong activity against phytopathogenic fungi. In this contribution, we report on the unprecedented N-acyl-tetrapeptide structure and antifungal potency of this natural product. We further provide insights into central steps of its biosynthesis mediated by a nonclassical nonribosomal peptide synthesis machinery lacking condensation domains. With the involvement of a sole acyl/peptidyl carrier protein AfcK, an acyltransferase AfcL and coenzyme A, the growing acyl-peptide chain is shuffled between different thioester carriers during the intricate biosynthetic assembly. The knowledge of the AFC-BC11 structure may contribute to the development of antifungals against phytopathogens and, with the afc gene cluster being conserved in various Burkholderia strains, possibly to an understanding of the human pathogenesis of the BCC.