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3drc

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[[Image:3drc.gif|left|200px]]
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{{STRUCTURE_3drc| PDB=3drc | SCENE= }}
{{STRUCTURE_3drc| PDB=3drc | SCENE= }}
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'''INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS'''
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===INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS===
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==Overview==
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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.
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{{ABSTRACT_PUBMED_1932031}}
==About this Structure==
==About this Structure==
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[[Category: Oatley, S J.]]
[[Category: Oatley, S J.]]
[[Category: Oxidoreductase]]
[[Category: Oxidoreductase]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 22:00:31 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 29 01:28:08 2008''

Revision as of 22:28, 28 July 2008

Image:3drc.png

Template:STRUCTURE 3drc

INVESTIGATION OF THE FUNCTIONAL ROLE OF TRYPTOPHAN-22 IN ESCHERICHIA COLI DIHYDROFOLATE REDUCTASE BY SITE-DIRECTED MUTAGENESIS

Template:ABSTRACT PUBMED 1932031

About this Structure

3DRC 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

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