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1a71

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{{STRUCTURE_1a71| PDB=1a71 | SCENE= }}
{{STRUCTURE_1a71| PDB=1a71 | SCENE= }}
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'''TERNARY COMPLEX OF AN ACTIVE SITE DOUBLE MUTANT OF HORSE LIVER ALCOHOL DEHYDROGENASE, PHE93=>TRP, VAL203=>ALA WITH NAD AND TRIFLUOROETHANOL'''
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===TERNARY COMPLEX OF AN ACTIVE SITE DOUBLE MUTANT OF HORSE LIVER ALCOHOL DEHYDROGENASE, PHE93=>TRP, VAL203=>ALA WITH NAD AND TRIFLUOROETHANOL===
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==Overview==
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The oxidation of alcohol to aldehyde by horse liver alcohol dehydrogenase (LADH) requires the transfer of a hydride ion from the alcohol substrate to the cofactor nicotinamide adenine dinucleotide (NAD). A quantum mechanical tunneling contribution to this hydride transfer step has been demonstrated in a number of LADH mutants designed to enhance or diminish this effect [Bahnson, B. J., et al. (1997) Proc. Natl. Acad. Sci. U.S.A. 94, 12797-12802]. The active site double mutant Phe93 --&gt; Trp/Val203 --&gt; Ala shows a 75-fold reduction in catalytic efficiency relative to that of the native enzyme, and reduced tunneling relative to that of either single mutant. We present here two crystal structures of the double mutant: a 2.0 A complex with NAD and the substrate analogue trifluoroethanol and a 2.6 A complex with the isosteric NAD analogue CPAD and ethanol. Changes at the active site observed in both complexes are consistent with reduced activity and tunneling. The NAD-trifluoroethanol complex crystallizes in the closed conformation characteristic of the active enzyme. However, the NAD nicotinamide ring rotates away from the substrate, toward the space vacated by replacement of Val203 with the smaller alanine. Replacement of Phe93 with the larger tryptophan also produces unfavorable steric contacts with the nicotinamide carboxamide group, potentially destabilizing hydrogen bonds required to maintain the closed conformation. These contacts are relieved in the second complex by rotation of the CPAD pyridine ring into an unusual syn orientation. The resulting loss of the carboxamide hydrogen bonds produces an open conformation characteristic of the apoenzyme.
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(as it appears on PubMed at http://www.pubmed.gov), where 9649310 is the PubMed ID number.
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{{ABSTRACT_PUBMED_9649310}}
==About this Structure==
==About this Structure==
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[[Category: Ladh]]
[[Category: Ladh]]
[[Category: Liver]]
[[Category: Liver]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 09:54:42 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 16:16:47 2008''

Revision as of 13:16, 30 June 2008

Image:1a71.png

Template:STRUCTURE 1a71

TERNARY COMPLEX OF AN ACTIVE SITE DOUBLE MUTANT OF HORSE LIVER ALCOHOL DEHYDROGENASE, PHE93=>TRP, VAL203=>ALA WITH NAD AND TRIFLUOROETHANOL

Template:ABSTRACT PUBMED 9649310

About this Structure

1A71 is a Single protein structure of sequence from Equus caballus. Full crystallographic information is available from OCA.

Reference

Active site modifications in a double mutant of liver alcohol dehydrogenase: structural studies of two enzyme-ligand complexes., Colby TD, Bahnson BJ, Chin JK, Klinman JP, Goldstein BM, Biochemistry. 1998 Jun 30;37(26):9295-304. PMID:9649310

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