Investigation of the functional role of tryptophan-22 in Escherichia coli dihydrofolate reductase by site-directed mutagenesis.Warren, M.S., Brown, K.A., Farnum, M.F., Howell, E.E., Kraut, J.
(1991) Biochemistry 30: 11092-11103
- PubMed: 1932031
- Primary Citation of Related Structures:
- PubMed Abstract:
- 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
- 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 Structure of Unliganded Escherichia Coli Dihydrofolate Reductase. Ligand-Induced Conformational Changes and Cooperativity in Binding
Bystroff, C.,Kraut, J.
(1991) Biochemistry 30: 2227
- 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 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
We have applied site-directed mutagenesis methods to change the conserved tryptophan-22 in the substrate binding site of Escherichia coli dihydrofolate reductase to phenylalanine (W22F) and histidine (W22H). The crystal structure of the W22F mutant i ...
We have applied site-directed mutagenesis methods to change the conserved tryptophan-22 in the substrate binding site of Escherichia coli dihydrofolate reductase to phenylalanine (W22F) and histidine (W22H). The crystal structure of the W22F mutant in a binary complex with the inhibitor methotrexate has been refined at 1.9-A resolution. The W22F difference Fourier map and least-squares refinement show that structural effects of the mutation are confined to the immediate vicinity of position 22 and include an unanticipated 0.4-A movement of the methionine-20 side chain. A conserved bound water-403, suspected to play a role in the protonation of substrate DHF, has not been displaced by the mutation despite the loss of a hydrogen bond with tryptophan-22. Steady-state kinetics, stopped-flow kinetics, and primary isotope effects indicate that both mutations increase the rate of product tetrahydrofolate release, the rate-limiting step in the case of the wild-type enzyme, while slowing the rate of hydride transfer to the point where it now becomes at least partially rate determining. Steady-state kinetics show that below pH 6.8, kcat is elevated by up to 5-fold in the W22F mutant as compared with the wild-type enzyme, although kcat/Km(dihydrofolate) is lower throughout the observed pH range. For the W22H mutant, both kcat and kcat/Km(dihydrofolate) are substantially lower than the corresponding wild-type values. While both mutations weaken dihydrofolate binding, cofactor NADPH binding is not significantly altered. Fitting of the kinetic pH profiles to a general protonation scheme suggests that the proton affinity of dihydrofolate may be enhanced upon binding to the enzyme. We suggest that the function of tryptophan-22 may be to properly position the side chain of methionine-20 with respect to N5 of the substrate dihydrofolate.
Department of Chemistry, University of California, San Diego, La Jolla 92093.