X-ray crystallographic evidence for the presence of the cysteine tryptophylquinone cofactor in L-lysine ε-oxidase from Marinomonas mediterranea

We have determined the x-ray crystal structure of L-lysine ε-oxidase from Marinomonas mediterranea in its native and L-lysine-complex forms at 1.94- and 1.99-Å resolution, respectively. In the native enzyme, electron densities clearly indicate the presence of cysteine tryptophylquinone (CTQ) previously identified in quinohemoprotein amine dehydrogenase. In the L-lysine-complex, an electron density corresponding to the bound L-lysine shows that its ε-amino group is attached to the C6 carbonyl group of CTQ, suggesting the formation of a Schiff-base intermediate. Collectively, the present crystal structure provides the first example of an enzyme employing a tryptophylquinone cofactor in an amine oxidase.