Recognition of structurally diverse substrates by type II 3-hydroxyacyl-CoA dehydrogenase (HADH II)/amyloid-beta binding alcohol dehydrogenase (ABAD)

Human type II hydroxyacyl-CoA dehydrogenase/amyloid-beta binding alcohol de hydrogenase (HADH II/ABAD) is an oxidoreductase whose salient features incl ude broad substrate specificity, encompassing 3-hydroxyacyl-CoA derivatives , hydroxysteroids, alcohols and beta -hydroxybutyrate, and the capacity to bind amyloid-beta peptide, leading to propagation of amyloid-induced cell s tress. In this study, we examine the structure and enzymatic activity of th e homologous rat HADH II/ABAD enzyme. We report the crystal structure of ra t HADH II/ABAD as a binary complex with its NADH cofactor to 2.0 A resoluti on, as a ternary complex with NAD(+) and 3-ketobutyrate (acetoacetate) to 1 .4 Angstrom resolution, and as a ternary complex with NADH and 17 beta -est radiol to 1.7 Angstrom resolution. This first crystal structure of an HADH II confirms these enzymes are closely related to the short-chain hydroxyste roid dehydrogenases and differ substantially from the classic, type I 3-hyd roxyacyl-CoA dehydrogenases. Binding of the ketobutyrate substrate is accom panied by closure of the active site specificity loop, whereas the steroid substrate does not appear to require closure for binding. Despite the diffe rent chemical nature of the two bound substrates, the presentation of chemi cal groups within the active site of each complex is remarkably similar, al lowing a general mechanism for catalytic activity to be proposed. There is a characteristic extension to the active site that is likely to accommodate the CoA moiety of 3-hydroxyacyl-CoA substrates. Rat HADH II/ABAD also bind s amyloid-beta (1-40) peptide with a K-D of 21 nM, which is similar to the interaction exhibited between this peptide and human HADH II/ABAD. These st udies provide the first structural insights into HADH II/ABAD interaction w ith its substrates, and indicate the relevance of the rodent enzyme and ass ociated rodent models for analysis of HADH II/ABAD's physiologic and pathop hysiologic properties. (C) 2000 Academic Press.