Raj SB, Ramaswamy S, Plapp BV

Yeast (Saccharomyces cerevisiae) alcohol dehydrogenase I (ADH1) is the constitutive enzyme that reduces acetaldehyde to ethanol during fermentation of glucose. ADH1 is a homotetramer of subunits with 347 amino acid residues. A structure for ADH1 was determined by X-ray crystallography at 2.44 A resolution. The asymmetric unit contains four different ...

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subunits, arranged as similar dimers named AB and CD. The unit cell contains two different tetramers made up of "back-to-back" dimers, AB:AB and CD:CD. The A and C subunits in each dimer are structurally similar, with a closed conformation and bound coenzyme, and the 2,2,2-trifluoroethanol oxygen is ligated to the catalytic zinc in the classical tetrahedral coordination with Cys-43, Cys-153, and His-66. In contrast, the B and D subunits have an open conformation with no bound coenzyme, and the catalytic zinc has an alternative, inverted coordination with Cys-43, Cys-153, His-66 and the carboxylate of Glu-67. The asymmetry in the dimeric subunits of the tetramer provides two structures that appear to be relevant for the catalytic mechanism, even if there is no evidence of cooperativity in binding of coenzyme and kinetics. The alternative coordination of the zinc may represent an intermediate in the mechanism of displacement of the zinc-bound water with alcohol or aldehyde substrates. Substitution of Glu-67 with Gln-67 decreases catalytic efficiency by 100-fold. Previous studies on structural modeling, evolutionary relationships, substrate specificity, chemical modification and site-directed mutagenesis are interpreted more fully with the three-dimensional structure.

Date: Aug. 26, 2014

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