2drc
From Proteopedia
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'''INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS''' | '''INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS''' | ||
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[[Category: Brown, K A.]] | [[Category: Brown, K A.]] | ||
[[Category: Kraut, J.]] | [[Category: Kraut, J.]] | ||
| - | [[Category: | + | [[Category: Oxidoreductase]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 01:00:16 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 22:00, 3 May 2008
INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS
Overview
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.
About this Structure
2DRC is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Investigation of the functional role of tryptophan-22 in Escherichia coli dihydrofolate reductase by site-directed mutagenesis., Warren MS, Brown KA, Farnum MF, Howell EE, Kraut J, Biochemistry. 1991 Nov 19;30(46):11092-103. PMID:1932031 Page seeded by OCA on Sun May 4 01:00:16 2008
