The curacins, mixed polyketide-nonribosomal peptide natural products isolated from the cyanobacterium Moorea producens, showcase interesting structural features and antineoplastic properties. Their biosynthetic pathway offers a unique look in polyketide dehydratase (DH) activity owing to their rich variety of olefins (terminal, di-, and trisubstituted with both E- and Z-geometries). Moreover, the elucidation of the gene cluster responsible for curacin biosynthesis has revealed a wrinkle in the previously presumed straightforward production: a lack of DH domains compared to predicted activity (Figure 1). Structure-based retro-biosynthesis forecasts that curacin modules G, H, I, J, and K should have dehydratase domains, but only H, J, and K contain DH signature sequences. Furthermore, module F (a module with no anticipated dehydration event) houses a DH domain. This conundrum may have one of three explanations. Two modules may form a protein-protein interaction so that a single DH domain may accomplish dehydration in two or more steps of the pathway. Alternatively, a trans-acting dehydratase encoded outside of the curacin modules acts on one or more modules maturing intermediate(s). Finally, the dehydrations may be atypical γ, δ-eliminations catalyzed by the following DH domains. We have synthesized N-acetylcysteamine thioester analogs of several predicted DH events and have carried out rigorous kinetic evaluation with heterologously produced curacin dehydratase domains, in an effort to determine their innate substrate selectivity. Through study of domain-domain interactions and native domain substrate biases we hope to unravel how nature sets curacin olefin geometry and how similar variations may take place in other polyketide natural products.

Curacin biosynthesis: A model for unexpected dehydatase domain activity

249th National Meeting (2015)

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