title: Modeling studies of conformational changes in the substrate-binding loop in Drosophila alcohol dehydrogenase.
abstract: Three-dimensional structures of seven short-chain dehydrogenases/reductases show that these enzymes share common structural features. Sequence alignment studies of Drosophila alcohol dehydrogenase (DADH), with an unknown 3D-structure, and four short-chain dehydrogenases/reductases with known X-ray structures suggest that DADH shares the same structural features. However, the substrate binding regions, which are located in the C-terminal region of these enzymes, share little sequence homology, because of the wide variety of substrates used. X-ray structures of short-chain dehydrogenases/reductases indicate that conformational changes occur in a loop, in the C-terminal region, upon substrate binding. This substrate-binding loop is located between a strand and a helix and may contain one or two small helices. Secondary structure predictions and modeling studies of this substrate-binding loop in DADH predict that the two helices may also be present in this enzyme. The naturally occurring variants of Drosophila melanogaster alleloenzymes ADH-S and ADH-F differ in a replacement of threonine by lysine at position 192, which is located at a central position in the substrate-binding loop. The positive charge of lysine may move significantly on substrate binding, resulting in a direct charge interaction with NAD+ in the enzyme-substrate complex, explaining a very strong influence of pH on the binding of ADH-S for the NAD+ analogue Cibacron Blue. This indicates that the ADH S/F polymorphism has a direct influence on the catalytic properties of the enzyme.
authors.affiliation: Department of Biochemistry, University of Groningen, The Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Smilda
authors.forename: P
authors.initials: P
authors.lastname: Reinders
authors.forename: J J
authors.initials: JJ
authors.lastname: Beintema
mesh_terms: D000426:Alcohol Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000429:Alcohol Oxidoreductases / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004330:Drosophila / Q000201:enzymology*; D006913:Hydroxysteroid Dehydrogenases / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D011110:Polymorphism, Genetic; D011487:Protein Conformation; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid
chemical_list: D009243:NAD; D000429:Alcohol Oxidoreductases; D006913:Hydroxysteroid Dehydrogenases; D000426:Alcohol Dehydrogenase; C025376:7 alpha-hydroxysteroid dehydrogenase