Tyrosinase (EC 1.14.18.1) is a
copper-containing
enzyme that catalyzes several reactions in the biosynthesis of
melanin pigments and is deficient in patients with type I
oculocutaneous albinism (OCA1).
Tyrosinase is thought to bind two
copper ions, one at each of two conserved sequence motifs, termed CuA and CuB, but to date this has been directly proved only for the Neurospora and mushroom
enzyme. Here, we demonstrate that mammalian
tyrosinase directly binds
copper, and that the CuA and CuB sites are both required for
copper binding and for catalytic activity. We show that in human
tyrosinase,
copper binding by the CuB site is most likely coordinated by residues His363, His367, and His389, and that
copper binding may be cooperative, with
copper binding at one site facilitating
copper binding by the other site. Furthermore, correct folding of the
tyrosinase polypeptide appears to be necessary for
copper binding, and a number of human OCA1 mutations disrupt
copper binding and thus catalytic function of
tyrosinase.