J. Biol. Chem., Vol. 266, Issue 30, 19890-19893, Oct, 1991
Trimethoprim binds in a bacterial mode to the wild-type and E30D mutant of mouse dihydrofolate reductase
CR Groom, J Thillet, AC North, R Pictet and AJ Geddes
Department of Biochemistry and Molecular Biology, University of Leeds, United Kingdom.
Previous crystallographic studies of the antibacterial trimethoprim in
complexes with bacterial and avian dihydrofolate reductases have shown
substantial differences in the mode of binding, providing plausible
explanations for the origin of the remarkable species selectivity of this
inhibitor (Matthews, D. A., Bolin, J. T., Burridge, J. M., Filman, D. J.,
Volz, K. W., Kaufman, B. T., Beddell, C. R., Champness, J. N., Stammers, D.
K., and Kraut, J. (1985) J. Biol. Chem. 260, 381-391; Matthews, D. A.,
Bolin, J. T., Burridge, J. M., Filman, D. J., Volz, K. W., and Kraut, J.
(1985) J. Biol. Chem. 260, 392-399). A major species difference between the
active sites is that the only carboxylate present is always Glu in
vertebrates and Asp in bacteria. Crystallographic studies of the wild-type
and E30D mutant of the enzyme from mouse now reveal that in both cases
trimethoprim is bound in an identical fashion to that observed with the
bacterial enzyme, and there is no obvious single explanation for the origin
of the 10(5)-fold selectivity of trimethoprim binding. In an earlier study
of a mouse wild-type enzyme using more limited data it was proposed that
trimethoprim bound in the avian mode (Stammers, D. K., Champness, J. N.,
Beddell, C. R., Dann, J. G., Eliopoulos, E. E., Geddes, A. J., Ogg, D., and
North, A. C. T. (1987) FEBS Lett. 218, 178-184), but a re- examination
indicates that the occupancy of the active site by trimethoprim is less
than had been thought, and we are currently unable to make an unambiguous
interpretation of the electron density maps and cannot confirm the avian
mode of binding in those crystals.