1qv6

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spinqualitylabelsall models 1qv6, resolution 1.80Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

HORSE LIVER ALCOHOL DEHYDROGENASE HIS51GLN/LYS228ARG MUTANT COMPLEXED WITH NAD+ AND 2,4-DIFLUOROBENZYL ALCOHOL

Overview

Histidine-51 in horse liver alcohol dehydrogenase (ADH) is part of a, hydrogen-bonded system that appears to facilitate deprotonation of the, hydroxyl group of water or alcohol ligated to the catalytic zinc. The, contribution of His-51 to catalysis was studied by characterizing ADH with, His-51 substituted with Gln (H51Q). The steady-state kinetic constants for, ethanol oxidation and acetaldehyde reduction at pH 8 are similar for, wild-type and H51Q enzymes. In contrast, the H51Q substitution, significantly shifts the pH dependencies for steady-state and transient, reactions and decreases by 11-fold the rate constant for the transient, oxidation of ethanol at pH 8. Modest substrate deuterium isotope effects, indicate that hydride transfer only partially limits the transient, oxidation and turnover. Transient data show that the H51Q substitution, significantly decreases the rate of isomerization of the enzyme-NAD(+), complex and becomes a limiting step for ethanol oxidation. Isomerization, of the enzyme-NAD(+) complex is rate limiting for acetaldehyde reduction, catalyzed by the wild-type enzyme, but release of alcohol is limiting for, the H51Q enzyme. X-ray crystallography of doubly substituted, His51Gln:Lys228Arg ADH complexed with NAD(+) and 2,3- or, 2,4-difluorobenzyl alcohol shows that Gln-51 isosterically replaces, histidine in interactions with the nicotinamide ribose of the coenzyme and, that Arg-228 interacts with the adenosine monophosphate of the coenzyme, without affecting the protein conformation. The difluorobenzyl alcohols, bind in one conformation. His-51 participates in, but is not essential, for, proton transfers in the mechanism.

About this Structure

1QV6 is a Single protein structure of sequence from Equus caballus with ZN, NAD, 24B and MPD as ligands. Active as Alcohol dehydrogenase, with EC number 1.1.1.1 Full crystallographic information is available from OCA.

Reference

Participation of histidine-51 in catalysis by horse liver alcohol dehydrogenase., LeBrun LA, Park DH, Ramaswamy S, Plapp BV, Biochemistry. 2004 Mar 23;43(11):3014-26. PMID:15023053

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