Christopher Raymond Beddell

The structure of mouse L1210 dihydrofolate reductase-drug complexes and the construction of a model of human enzyme

The structure of mouse L1210 dihydrofolate reductase (DHFR) complexed with NADPH and trimethoprim has been refined at 2.0 Å resolution. The analogous complex with NADPH and methotrexate has been refined at 2.5 Å resolution. These structures reveal for the first time details of drug interactions with a mammalian DHFR, which are compared with those observed from previous X‐ray investigations of DHFR/inhibitor complexes. The refined L1210 structure has been used as the basis for the construction of a model of the human enzyme. There are only twenty‐one sequence differences between mouse L1210 and human DHFRs, and all but two of these are located close to the molecular surface: a strong indication that the active sites are essentially identical in these two mammalian enzymes.

Crystallographic investigation of the cooperative interaction between trimethoprim, reduced cofactor and dihydrofolate reductase

The structure of the complex between E. coli (RT500) form I dihydrofolate reductase, the antibacterial trimethoprim and NADPH has been determined by X‐ray crystallography. The inhibitor and cofactor are in mutual contact. A flexible chain segment which includes Met 20 is in contact with the inhibitor in the presence of NADPH, but more distant in its absence. By contrast, the inhibitor conformation is little changed with NADPH present. We discuss these observations with regard to the mutually cooperative binding of these ligands to the protein, and to the associated enhancement of inhibitory selectivity shown by trimethoprim for bacterial as opposed to vertebrate enzyme.