Autori: Gertrude-E. Costin, Julio C. Valencia, Kazumasa Wakamatsu, Shosuke Ito, Wilfred D. Vieira, Yuji Yamaguchi, Adina L. Milac, François Rouzaud, Andrei-J. Petrescu, M. Lynn Lamoreux, Vincent J. Hearing

Editorial: Biochem. J., 391 (2), p.249-259, 2005.

Rezumat:

Dopachrome tautomerase (Dct) is a type I membrane protein and an important regulatory enzyme that plays a pivotal role in the biosynthesis of melanin and in the rapid metabolism of its toxic intermediates. Dct-mutant melanocytes carrying the slaty or slaty light mutations were derived from the skin of newborn congenic C57BL/6J non-agouti black mice and were used to study the effect(s) of these mutations on the intracellular trafficking of Dct and on the pigmentation of the cells. Dct activity is 3-fold lower in slaty cells compared with non-agouti black melanocytes, whereas slaty light melanocytes have a surprisingly 28-fold lower Dct activity. Homology modelling of the active site of Dct suggests that the slaty mutation [R194Q (Arg194–>Gln)] is located in the active site and may alter the ability of the enzyme to transform the substrate. Transmembrane prediction methods indicate that the slaty light mutation [G486R (Gly486–>Arg)] may result in the sliding of the transmembrane domain towards the N-terminus, thus interfering with Dct function. Chemical analysis showed that both Dct mutations increase pheomelanin and reduce eumelanin produced by melanocytes in culture. Thus the enzymatic activity of Dct may play a role in determining whether the eumelanin or pheomelanin pathway is preferred for pigment biosynthesis.

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