CRYSTAL STRUCTURE OF A EUKARYOTIC (PEA SEEDLING) COPPER-CONTAINING AMINE OXIDASE AT 2.3 RESOLUTION. Vinay Kumar, Hans C. Freeman and J. Mitchell Guss (University of Sydney, NSW 2006, Australia); David M. Dooley and Michele A. McGuirl (Montana State University, Bozeman, MT 50717, USA.)

We report the first structure analysis of a eukaryotic amine oxidase, pea seedling amine oxidase (PSAO), at 2.3 resolution. The structure was solved using phases derived from a single heavy-atom (phosphotungstic acid, H₃PW₁₂O₄₀) derivative. The positions of the tungsten atoms in the W₁₂ cluster were obtained by molecular replacement using the prokaryotic amine oxidase from E. coli (ECAO) [Parsons, M.R. et al. (1995). Structure, 3, 1171-1184] as a search model. However, the methodology avoided bias from the search model and resulted in an essentially independent view of a eukaryotic amine oxidase molecule.

Copper-containing amine oxidases are a widely distributed class of enzyme whose function is to catalyze the oxidative deamination of biogenic amines to the corresponding aldehyde. The redox reaction is facilitated by an organic cofactor, topa quinone (TPQ), which is formed by the post-translational modification of an invariant Tyr residue.

The PSAO molecule is a homodimer with dimensions 100x63x42 ³. The copper(II) atom at the active site of each subunit is coordinated by three histidine side chains and two water molecules in an approximately square-pyramidal arrangement. All the atoms of the topa quinone (TPQ) cofactor are unambiguously defined. The closest contact to the copper atom is ~6. A second metal atom revealed by the structure analysis is tentatively identified as manganese(II).

The molecular structure of PSAO is similar to that of the prokaryotic ECAO. A detailed comparison of the two structures suggests that the TPQ side chain is sufficiently flexible to move between uncoordinated and coordinated positions with respect to the copper atom. Such flexibility may be associated with the different spatial requirements for TPQ biogenesis and amine oxidation.