CRYSTAL-STRUCTURE OF A QUINOENZYME - COPPER AMINE OXIDASE OF ESCHERICHIA-COLI AT 2-ANGSTROM RESOLUTION

Background: Copper amine oxidases are a ubiquitous and novel group of quinoenzymes that catalyze the oxidative deamination of primary amines to the corresponding aldehydes, with concomitant reduction of molecul ar oxygen to hydrogen peroxide. The enzymes are dimers of identical 70 -90 kDa subunits, each of which contains a single copper ion and a cov alently bound cofactor formed by the post-translational modification o f a tyrosine side chain to 2,4,5-trihydroxyphenylalanine quinone (TPQ) . Results: The crystal structure of amine oxidase from Escherichia col i has been determined in both an active and an inactive form. The only structural differences are in the active site, where differences in c opper coordination geometry and in the position and interactions of th e redox cofactor, TPQ, are observed. Each subunit of the mushroom-shap ed dimer comprises four domains: a 440 amino acid C-terminal beta sand wich domain, which contains the active site and provides the dimer int erface, and three smaller peripheral alpha/beta domains (D1-D3), each of about 100 amino acids. D2 and D3 show remarkable structural and seq uence similarity to each other and are conserved throughout the quinoe nzyme family. In contrast, D1 is absent from some amine oxidases. The active sites are well buried from solvent and lie some 35 Angstrom apa rt, connected by a pair of beta hairpin arms. Conclusions: The crystal structure of E. coli copper amine oxidase reveals a number of unexpec ted features and provides a basis for investigating the intriguing sim ilarities and differences in catalytic mechanism of members of this en zyme family. In addition to the three conserved histidines that bind t he copper, our studies identify a number of other conserved residues c lose to the active site, including a candidate for the catalytic base and a fourth conserved histidine which is involved in an interesting i ntersubunit interaction.