title: Mutations in dopachrome tautomerase (Dct) affect eumelanin/pheomelanin synthesis, but do not affect intracellular trafficking of the mutant protein.
abstract: 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.
authors.affiliation: Pigment Cell Biology Section, Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health (NIH), Bethesda, MD 20892, USA.
authors.forename: Gertrude-E
authors.initials: GE
authors.lastname: Costin
authors.forename: Julio C
authors.initials: JC
authors.lastname: Valencia
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Wakamatsu
authors.forename: Shosuke
authors.initials: S
authors.lastname: Ito
authors.forename: Francisco
authors.initials: F
authors.lastname: Solano
authors.forename: Adina L
authors.initials: AL
authors.lastname: Milac
authors.forename: Wilfred D
authors.initials: WD
authors.lastname: Vieira
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: François
authors.initials: F
authors.lastname: Rouzaud
authors.forename: Andrei-J
authors.initials: AJ
authors.lastname: Petrescu
authors.forename: M Lynn
authors.initials: ML
authors.lastname: Lamoreux
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Hearing
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic; D019746:Intramolecular Oxidoreductases / Q000235:genetics* / Q000378:metabolism*; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D011487:Protein Conformation; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid
chemical_list: D008543:Melanins; C018362:pheomelanin; C041877:eumelanin; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase