Structural studies of copper amine oxidase

Introduction Copper amine oxidases are ubiquitous metalloenzymes. Their function in prokaryotes and lower eukaryotes is to utilise amines as a source for carbon and nitrogen. In higher eukaryotes, their roles are less well understood, but have been linked with cell signalling, growth and development, and cell death. Despite this apparent diversity, their fundamental role is to catalyse the oxidation of primary amine substrates to their corresponding aldehydes. Amine oxidases are homodimeric enzymes ranging in size from 140-180 kDa. We work on copper amine oxidase from Escherichia coli (ECAO); the crystal structure of which has been determined to 2.0 Å. Each subunit consists of four distinct domains and contains a single copper ion and a quinone cofactor, 2,4,5trihydroxyphenylalanine quinone (TPQ) at the active site. Also found at the active site are three histidine residues and one or two water molecules in an approximate square pyramidal arrangement around the copper. The TPQ cofactor is generated from an intrinsic tyrosine in the amino acid sequence by a self-processing event that requires only the bound copper ion and molecular oxygen. This cofactor is quite mobile, being able to swing around to adopt different conformations. Copper amine oxidases have highly conserved active sites, with differences occurring mainly from TPQ mobility and position. A key factor in the biogenesis of the TPQ is the copper ion, which also plays an important function in the catalytic mechanism.