Molecular Dynamics Pinpoint the Global Fluorine Effect in Balanoid Binding to PKC epsilon and PKA

(-)-Balanol is an adenosine triphosphate mimic that inhibits protein kinase C (PKC) isozymes and cAMP-dependent protein kinase (PKA) with limited selectivity. While PKA is known as a tumor promoter, PKC isozymes can be tumor promoters or suppressors. In particular, PKC epsilon is frequently involved in tumorigenesis and a potential target for anticancer drugs. We recently reported that stereospecific fluorination of balanol yielded a balanoid with enhanced selectivity for PKC epsilon over other PKC isozymes and PKA, although the global fluorine effect behind the selectivity enhancement is not fully understood. Interestingly, in contrast to PKA, PKC epsilon is more sensitive to this fluorine effect. Here we investigate the global fluorine effect on the different binding responses of PKC epsilon and PKA to balanoids using molecular dynamics (MD) simulations. For the first time to the best of our knowledge, we found that a structurally equivalent residue in each kinase, Thr184 in PKA and Ala549 in PKC epsilon, is essential for the different binding responses. Furthermore, the study revealed that the invariant Lys, Lys73 in PKA and Lys437 in PKC epsilon, already known to have a crucial role in the catalytic activity of kinases, serves as the main anchor for balanol binding. Overall, while Thr184 in PKA attenuates the effect of fluorination, Ala549 permits remote response of PKC epsilon to fluorine substitution, with implications for rational design of future balanol-based PKC epsilon inhibitors.