The crystal structure of unliganded dihydrofolate reductase (DHFR) from Escherichia coli has been solved and refined to an R factor of 19% at 2.3-A resolution in a crystal form that is nonisomorphous with each of the previously reported E. coli DHFR ...
The crystal structure of unliganded dihydrofolate reductase (DHFR) from Escherichia coli has been solved and refined to an R factor of 19% at 2.3-A resolution in a crystal form that is nonisomorphous with each of the previously reported E. coli DHFR crystal structures [Bolin, J. T., Filman, D. J., Matthews, D. A., Hamlin, B. C., & Kraut, J. (1982) J. Biol. Chem. 257, 13650-13662; Bystroff, C., Oatley, S. J., & Kraut, J. (1990) Biochemistry 29, 3263-3277]. Significant conformational changes occur between the apoenzyme and each of the complexes: the NADP+ holoenzyme, the folate-NADP+ ternary complex, and the methotrexate (MTX) binary complex. The changes are small, with the largest about 3 A and most of them less than 1 A. For simplicity a two-domain description is adopted in which one domain contains the NADP+ 2'-phosphate binding site and the binding sites for the rest of the coenzyme and for the substrate lie between the two domains. Binding of either NADP+ or MTX induces a closing of the PABG-binding cleft and realignment of alpha-helices C and F which bind the pyrophosphate of the coenzyme. Formation of the ternary complex from the holoenzyme does not involve further relative domain shifts but does involve a shift of alpha-helix B and a floppy loop (the Met-20 loop) that precedes alpha B. These observations suggest a mechanism for cooperativity in binding between substrate and coenzyme wherein the greatest degree of cooperativity is expressed in the transition-state complex. We explore the idea that the MTX binary complex in some ways resembles the transition-state complex.
Related Citations:
Crystal Structures of Escherichia Coli and Lactobacillus Casei Dihydrofolate Reductase Refined at 1.7 Angstroms Resolution. II. Environment of Bound Nadph and Implications for Catalysis Filman, D.J.,Bolin, J.T.,Matthews, D.A.,Kraut, J. (1982) J.Biol.Chem. 257: 13663
Functional Role of Aspartic Acid-27 in Dihydrofolate Reductase Revealed by Mutagenesis Howell, E.E.,Villafranca, J.E.,Warren, M.S.,Oatley, S.J.,Kraut, J. (1986) Science 231: 1123
Crystal Structures of Escherichia Coli and Lactobacillus Casei Dihydrofolate Reductase Refined at 1.7 Angstroms Resolution. I. General Features and Binding of Methotrexate Bolin, J.T.,Filman, D.J.,Matthews, D.A.,Hamlin, R.C.,Kraut, J. (1982) J.Biol.Chem. 257: 13650
Crystal Structures of Escherichia Coli Dihydrofolate Reductase: The Nadp+ Holoenzyme and the Folate Nadp+ Ternary Complex. Substrate Binding and a Model for the Transition State Bystroff, C.,Oatley, S.J.,Kraut, J. (1990) Biochemistry 29: 3263
Crystal Structures of Recombinant Human Dihydrofolate Reductase Complexed with Folate and 5-Deazafolate Davies II, J.F.,Delcamp, T.J.,Prendergast, N.J.,Ashford, V.A.,Freisheim, J.H.,Kraut, J. (1990) Biochemistry 29: 9467
Organizational Affiliation:
Department of Chemistry, University of California, San Diego, La Jolla 92093.
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