Abstact

The quinone cofactor TPQ in copper amine oxidase is generated by posttranslational modification of an active site tyrosine residue. Using X-ray crystallography, we have probed the copper-dependent autooxidation process of TPQ in the enzyme from Arthrobacter globiformis. Apo enzyme crystals were anaerobically soaked with copper; the structure determined from this crystal provides a view of the initial state: the unmodified tyrosine coordinated to the bound copper. Exposure of the copper-bound crystals to oxygen led to the formation of freeze-trapped intermediates; structural analyses indicate that these intermediates contain dihydroxyphenylalanine quinone and trihydroxyphenylalanine. These are the first visualized intermediates during TPQ biogenesis in copper amine oxidase.