Dynamic dysfunction in dihydrofolate reductase results from antifolate drug binding: modulation of dynamics within a structural state.

The arduous task of rationally designing small-molecule enzyme inhibitors is complicated by the inherent flexibility of the protein scaffold. To gain insight into the changes in dynamics associated with small-molecule-based inhibition, we have characterized, using NMR spectroscopy, Escherichia coli dihydrofolate reductase in complex with two drugs: methotrexate and trimethoprim. The complexes allowed the intrinsic dynamic effects of drug binding to be revealed within the context of the "closed" structural ensemble. Binding of both drugs results in an identical decoupling of global motion on the micro- to millisecond timescale. Consistent with a change in overall dynamic character, the drugs' perturbations to pico- to nanosecond backbone and side-chain methyl dynamics are also highly similar. These data show that the inhibitors simultaneously modulate slow concerted switching and fast motions at distal regions of dihydrofolate reductase, providing a dynamic link between the substrate binding site and distal loop residues known to affect catalysis.