Liver alcohol dehydrogenase structure

The Protein Data Bank PDB ID 1A71 Colby T D Bahnson B J Chin J K Klinman J P Goldstein B M Active Site Modifications m a Double Mutant of Liver Alcohol Dehydrogenase Structural Studies of Two Enzyme Ligand Com plexes To be published... 

Colona-Cesari, F., Perahia, D., Karplus, M., Ecklund, H., Brandem, C. and Tapia, 0. (1986) Interdomain Motion in Liver Alcohol Dehydrogenase Structural and Energetic Analysis of the Hinge Bending Mode, J Biol. Chem. 261, 15273-15289. 

Active site modifications in a double mutant of liver alcohol dehydrogenase structural studies of two enzyme-ligand complexes. Biochemistry 37, 9295-9304. 

Eklund, H., et al. Three-dimensional structure of horse liver alcohol dehydrogenase at 2.4 A resolution. 

FIGURE 6.41 The quaternary structure of liver alcohol dehydrogenase. Within each subunit is a six-stranded parallel sheet. Between the two subunits is a two-stranded antiparallel sheet. The point in the center is a C9 symmetry axis. (Jane Richardson)... 

Zinc-containing alcohol dehydrogenases take up two electrons and a proton from alcohols in the form of a hydride. The hydride acceptor is usually NAD(P) (the oxidized form of nicotinamide adenine dinucleotide (NADH) or its phosphorylated derivative, NADPH). Several liver alcohol dehydrogenases have been structurally characterized, and Pig. 17.8 shows the environment around the catalytic Zn center and the bound NADH cofactor. 

Figure 17.8 Catal3ftic zinc center of horse liver alcohol dehydrogenase revealed from an X-ray crystallographic structure (PDB file 20HX) [Al-Karadaghi et al., 1994]. The bound NADH cofactor, a molecule of the inhibitor dimethylsulfoxide (DMSO), and the amino acid residues that coordinate the Zn are shown as sticks shaded according to the elements, and the Zn center is shown as a gray sphere, while the protein is shown in thin gray lines.

Al-Karadaghi S, Cedergren-Zeppezauert ES, HovmoUer S. 1994. Refined crystal structure of liver alcohol dehydrogenase-NADH complex at 1.8 A resolution. Acta Crystallogr DSO 793 - 807. 

For a liver alcohol dehydrogenase (LADH) model an NS2O coordination sphere is required. The chelating aldehydes are ideal for the formation of this donor set when combined with bis(pentafluoro-thiophenolato)zinc. Structural data on the complexes with one equivalent of 6-methylpyridine-2-carbaldehyde, 6-methoxypyridine-2-carbaldehyde, 2-(dimethylamino)benzal-dehyde) demonstrate that the coordination sphere for LADH has been reproduced to a close approximation and the corresponding alcohol complexes have also been characterized.354 Other thiophenols have been used to form such complexes but have not been structurally characterized.304... 

G. B. Strambini and M. Gonnelli, Effects of urea and guanidine hydrochloride on the activity and dynamical structure of equine liver alcohol dehydrogenase, Biochemistry 25, 2471-2476 (1986). 

Schneider, G., Eklund, H., Cedergren-Zeppezauer, E., and Zeppezauer, M. (1983). Crystal structures of the active site in specifically metal-depleted and cobalt-substituted horse liver alcohol dehydrogenase derivatives. Proc. Natl. Acad. Set. U.S.A. 80, 5289-5293. 

Alcohol dehydrogenases (ADH EC 1.1.1.1), for which several X-ray structures are available ", catalyze the biological oxidation of primary and secondary alcohols via the formal transfer of a hydride anion to the oxidized form of nicotinamide adenine dinucleotide (NAD ), coupled with the release of a proton. Liver alcohol dehydrogenase (LADH) consists of two similar subunits, each of which contains two zinc sites, but only one site within each subunit is catalytically active. The catalytic zinc is coordinated in a distorted tetrahedral manner to a histidine residue, two cysteine residues and a water molecule. The remaining zinc is coordinated tetrahedrally to four cysteine residues and plays only a structural role . 

The dimensions of cavities in enzymes differ considerably, depending on their physiological function. In many cases the clefts are occupied by clusters of organized water molecules. Such clusters can be seen in certain X-ray structures of enzymes (e.g., the structure of carboxypeptidase A determined by Lipscomb). If the clefts are deep, as in horse liver alcohol dehydrogenase, a channel for removal of water is present (Branden). 

For example, liver alcohol dehydrogenase was crystallized as the enzyme N AD1 p-bromobenzyl alcohol complex with saturating concentrations of substrates in an equilibrium mixture51b and studied at low resolution. Transient kinetic studies or direct spectroscopic determinations led to the conclusion that the internal equilibrium (E NAD alcohol = E NADH aldehyde) favors the NAD1 alcohol complex.52 Subsequently, the complex was studied at higher resolution, and the basic structural features were confirmed with a... 

Figure 15-5 Structure of the complex of horse liver alcohol dehydrogenase with NAD+ and the slow substrate p-bromobenzyl alcohol. The zinc atom and the nicotinamide ring of the bound NAD+ are shaded. Adjacent to them is the bound substrate. Courtesy of Bryce Plapp. Based on Ramaswamy et al.53...

A crystal structure of a ternary complex of horse liver alcohol dehydrogenase with NADH and the inhibitor, dimethyl sulfoxide, first at 4.5 A resolution1365 and a further refinement to 2.9 A resolution,1366 has been published by Eklund et al. The gross structure of the ternary complex is similar to that of the free enzyme structure. Each subunit is divided into a coenzyme-binding domain and a catalytic domain. The subunits are joined together near the... 

These enzymes, which mainly catalyze hydrolytic reactions, have the zinc ions at their active sites. However, Zn ions also appear necessary in some cases for stabilization of the protein structure, e.g. in Cu/Zn SOD, insulin, liver alcohol dehydrogenase and alkaline phosphatases. 

Figure 4.16. Graphic display of 3D structure with RasMol. The display shows the 3D structure of liver alcohol dehydrogenase complex (6ADH.pdb) with two subunits and bound NAD +. The protein molecule is visualized with RasMenu.

Cronin L, Walton PH (2003) Synthesis and structure of [Zn(OMe)(L)HZn(OH)(L)]-2(BPh4), L = ris.ris-1.3.5-tt i s / E)-3-(2-furyl)acrylideneamino cyclohcxanc structural models of carbonic anhydrase and liver alcohol dehydrogenase. Chem Commun 1572-1573... 

Horse liver alcohol dehydrogenase is a well-documented enzyme capable of operating with high stereoselectivity on a broad structural range of alcohol and carbonyl substrates. The present reaction proceeds via the pathway shown below, where NAD and NADH represent the oxidized and reduced forms, respectively, of the nicotinamide adenine dinucleotide coenzyme. 

It is also the case that enzymes showing sequence similarities do not necessarily catalyse the same reactions. Sheep liver sorbitol dehydrogenase (EC 1.1.1.14) does not utilize ethanol, though in primary structure it resembles both yeast and horse liver alcohol dehydrogenases [5,6]. 

The EE and SS isozymes of horse liver alcohol dehydrogenase have very similar primary structures [7,8]. Ethanol is a substrate for both, but both have a wide specificity, and ethanol is not the best substrate for either. The SS isozyme has 3/3-hydroxysteroid dehydrogenase activity [9,10], which the EE isozyme does not have, and which is thought to depend upon a single amino acid replacement [11], It remains to be established whether these different isozymes have different roles in vivo. 

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