Structural factors determining the binding selectivity of the antibacterial drug trimethoprim to dihydrofolate reductase

The structure of the complex of the antibacterial drug trimethoprim with its target, the enzyme dihydrofolate reductase (DHFR) of Lactobacillus casei, was studied using multidimensional NMR spectroscopy. Aseries of 33 high-resolution structures of this complex in solution was calculated using the measured experimental parameters of the nuclear Overhauser effect, spin-spin coupling constants, and residual dipolar coupling constants. The key interactions leading to stable binding of the drug with the enzyme were determined. The resulting structural data were compared with structures of the ternary complex of trimethoprim and the coenzyme NADPH with bacterial (L. casei) and human DHFR that were calculated previously. The most probable reasons for cooperative interaction of trimethoprim and NADPH that determine the highly selective binding of the drug to the bacterial enzyme, in particular, the protein conformation change on going from the binary to the ternary complex of DHFR, were discussed.