Predicted incorporation of non-native substrates by a polyketide synthase yields bioactive natural product derivatives.

The polyether ionophore monensin is biosynthesized by a polyketide synthase that delivers a mixture of monensins A and B by the incorporation of ethyl- or methyl-malonyl-CoA at its fifth module. Here we present the first computational model of the fifth acyltransferase domain (AT5mon ) of this polyketide synthase, thus affording an investigation of the basis of the relaxed specificity in AT5mon , insights into the activation for the nucleophilic attack on the substrate, and prediction of the incorporation of synthetic malonic acid building blocks by this enzyme. Our predictions are supported by experimental studies, including the isolation of a predicted derivative of the monensin precursor premonensin. The incorporation of non-native building blocks was found to alter the ratio of premonensins A and B. The bioactivity of the natural product derivatives was investigated and revealed binding to prenyl-binding protein. We thus show the potential of engineered biosynthetic polyketides as a source of ligands for biological macromolecules.

Cell-penetrating bisubstrate-based protein kinase C inhibitors.

Although protein kinase inhibitors present excellent pharmaceutical opportunities, lack of selectivity and associated therapeutic side effects are common. Bisubstrate-based inhibitors targeting both the high-selectivity peptide substrate binding groove and the high-affinity ATP pocket address this. However, they are typically large and polar, hampering cellular uptake. This paper describes a modular development approach for bisubstrate-based kinase inhibitors furnished with cell-penetrating moieties and demonstrates their cellular uptake and intracellular activity against protein kinase C (PKC). This enzyme family is a longstanding pharmaceutical target involved in cancer, immunological disorders, and neurodegenerative diseases. However, selectivity is particularly difficult to achieve because of homology among family members and with several related kinases, making PKC an excellent proving ground for bisubstrate-based inhibitors. Besides the pharmacological potential of the novel cell-penetrating constructs, the modular strategy described here may be used for discovering selective, cell-penetrating kinase inhibitors against any kinase and may increase adoption and therapeutic application of this promising inhibitor class.