W0377

Structural Basis for Ethanol Aversion: Disorder in Inactive Aldehyde Dehydrogenase 2. Heather N. Larson, Thomas D. Hurley, Indiana Univ. School of Medicine, Indianapolis, IN 46202.

The aldehyde dehydrogenase superfamily is a large, diverse family of enzymes that catalyze the oxidation of aldehydes to acids. Mitochondrial aldehyde dehydrogenase (ALDH2) is nuclear encoded and transported to the mitochondria where it catalyzes the oxidation of ethanol-derived acetaldehyde to acetate. The functional ALDH2 is a tetramer comprised of four identical subunits containing 500 amino acids each. A natural variant found in 40% of the East Asian population yields an amino acid change of Glu to Lys at position 487. This polymorphism is associated with an aversive response to alcohol consumption and is phenotypically dominant.

The tetramer is a dimer of dimers where the interface between subunits within a dimer is more extensive than the interface between the two dimers. Glu 487 is located in a loop at the dimer interface and forms hydrogen bounds with Arg 264 within the same subunit as well as Arg 475 in the neighboring subunit. We have solved the structure of the Asian variant in the presence and absence of cofactor. The apoenzyme structure is disordered in the area surrounding 475 and 487, although residue 487 itself is well ordered. The affected regions include an α-helix, a loop, and a β-strand at the dimer interface. In the cofactor-bound structure, these areas are more ordered. To further probe the interactions surrounding Glu 487, Arg 475 was mutated to Gln. This mutation yields an enzyme that exhibits positive cooperativity for NAD⁺-binding. We have solved the structure of this laboratory-created mutant in the presence and absence of cofactor and have observed disorder in the same regions as in the Asian variant, although to a lesser extent.

Both structures show that changes to the interactions near residue 487 lead to impaired cofactor binding due to structural disorder. This provides a mechanism for both the phenotypic dominance of the Asian variant and the observed cooperativity in the laboratory mutant. The difference in the ability of coenzyme binding to restore native-like activity is due to the extent of the disorder in the absence of coenzyme.