Investigation of the unusual biochemical transformations in cylindrocyclophane biosynthesis

Biosynthetic studies of natural products that have unique structures and functionalities often reveal remarkable enzymatic transformations. The cylindrocyclophanes are a family of natural products containing a rare paracyclophane carbon scaffold. With the goal of understanding the biochemical transformations involved in the cylindrocyclophane assembly, our group has sequenced the genome of C. licheniforme ATCC 29412, a producer of cylindrocyclophanes. Bioinformatic analysis of the genome sequence led to the discovery of a biosynthetic gene cluster responsible for the cylindrocyclophane assembly (cyl gene cluster). We validated the involvement of the cyl gene cluster in cylindrocyclophane production through characterization of biosynthetic enzymes and feeding studies using isotopically labeled compounds in the native producer. Through biochemical studies, we have shown that the cylindrocyclophane biosynthesis initiates with an activation of decanoic acid, followed by type I polyketide synthase (PKS) assembly line processing. A freestanding type III PKS terminates the assembly line by catalyzing the formation of a predicted monomeric unit of cylindrocyclophanes. In addition, the results from the feeding studies confirmed that decanoic acid is a precursor of the cylindrocyclophanes and that the cylindrocyclophane biosynthetic pathway involves functionalization of an unactivated C–H bond. Our current efforts focus on completing the characterization of the assembly line termination event and determining the enzymes involved in the aliphatic C–H bond activation and the key C–C bond formation. Elucidating the biosynthetic logic underlying construction of the unusual paracyclophane scaffold and subsequent tailoring events should enrich our understanding of how Nature builds complex organic molecules.