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 molecular oxygen to hydrogen peroxide. The enzymes are dimers of identical 70-90 kDa subunits, each of which contains a single copper ion and a covalently bound cofactor formed by the post-translational modification of a tyrosine side chain to 2,4,5-trihydroxyphenylalanine quinone (TPQ). Results The crystal structure of amine oxidase from Escherichia coli has been determined in both an active and an inactive form. The only structural differences are in the active site, where differences in copper coordination geometry and in the position and interactions of the redox cofactor, TPQ, are observed. Each subunit of the mushroom-shaped dimer comprises four domains: a 440 amino acid C-terminal β sandwich domain, which contains the active site and provides the dimer interface, and three smaller peripheral α/β domains (D1-D3), each of about 100 amino acids. D2 and D3 show remarkable structural and sequence similarity to each other and are conserved throughout the quinoenzyme family. In contrast, D1 is absent from some amine oxidases. The active sites are well buried from solvent and lie some 35 å apart, connected by a pair of β hairpin arms. Conclusion The crystal structure of E. coli copper amine oxidase reveals a number of unexpected features and provides a basis for investigating the intriguing similarities and differences in catalytic mechanism of members of this enzyme family. In addition to the three conserved histidines that bind the copper, our studies identify a number of other conserved residues close to the active site, including a candidate for the catalytic base and a fourth conserved histidine which is involved in an interesting intersubunit interaction.
Bibliographical noteFunding Information:
We thank RA Cooper and JP Porter for help in the early stages of the protein purification, JN Keen for N-terminal sequencing of the protein, D Ashworth for automated DNA sequencer operation and JP Klinman for discussions on the enzyme mechanism. We wish to thank E Duke, P Rizhkallah and the staff of Daresbury SRS for help with data collection and processing, BW Matthews for providing β-galactosidase coordinates and D Dixon for assistance in preparing the figures. BBSRC and EPSRC provided support for this research, including a Senior Visiting Fellowship to KDSY. SEVP is an International Scholar of the Howard Hughes Medical Institute and MJM was a Leverhulme Trust/Royal Society Senior Research Fellow.
Copyright 2014 Elsevier B.V., All rights reserved.
- 2,4,5-trihydroxyphenylalanine quinone
- amino acid derived cofactor
- copper amine oxidase