Structure and Biosynthesis of Myxofacyclines: Unique Myxobacterial Polyketides Featuring Varying and Unprecedented Heterocycles

A metabolome-guided screening approach in the novel myxobacterium Corallococcus sp. MCy9072 resulted in the isolation of the unprecedented natural product myxofacycline A featuring a rare isoxazole substructure. Identification and genomic investigation of additional producers alongside targeted gene inactivation experiments and heterologous expression of the corresponding biosynthetic gene cluster in the host Myxococcus xanthus DK1622 confirmed a noncanonical megaenzyme complex as the biosynthetic origin of myxofacycline A. Induced expression of the respective genes led to significantly increased production titers enabling the identification of six further members of the myxofacycline natural product family. Whereas myxofacycline A–D display an isoxazole substructure, myxofacycline E and F intriguingly were found to contain 4 pyrimidinole, a heterocycle unprecedented in natural products. Lastly, myxofacycline G features another rare 1,2 dihydropyrol-3-one moiety. In addition to the full structure elucidation, we report the underlying biosynthetic machinery and present a rationale for the formation of all myxofacyclines. Unexpectedly, an extraordinary polyketide synthase-nonribosomal peptide synthetase hybrid was found to produce all three types of heterocycles in these natural products.