Kobayashi T, Imokawa G, Bennett D C, Hearing V J
Laboratory of Cell Biology, NCI, National Institutes of Health, Bethesda Maryland 20892, USA.
J Biol Chem. 1998 Nov 27;273(48):31801-5. doi: 10.1074/jbc.273.48.31801.
Mammalian melanogenesis is regulated directly or indirectly by over 85 distinct loci. The Tyr/albino locus, in which mutations cause a lack of pigmentation, encodes tyrosinase (Tyr), the critical and rate-limiting melanogenic enzyme. Other melanogenic enzymes include Tyrp1 (or TRP1) and 3,4-dihydroxyphenylalanine-chrome tautomerase (Dct or TRP2) encoded at the Tyrp1/brown and Dct/slaty loci, respectively. Murine Tyrp1 can oxidize 5, 6-dihydroxyindole-2-carboxylic acid (DHICA) produced by Dct, but mutations in Tyrp1 also affect the catalytic functions of Tyr. All three enzymes are membrane-bound melanosomal proteins with similar structural features and are thought to interact within and stabilize a melanogenic complex. We have now further investigated the effect of a Tyrp1(b) mutation on Tyr stability. Pulse/chase labeling experiments show that Tyr is degraded more quickly in Tyrp1(b) mutant melanocytes than in melanocytes wild type at that locus. This reduced stability of Tyr can be partly rescued by infection with the wild type Tyrp1 gene, and this is accompanied by phenotypic rescue of infected melanocytes. In sum, these results suggest that, in addition to its catalytic function in oxidizing DHICA, Tyrp1 may play an important role in stabilizing Tyr, a second potential role in the regulation of melanin formation.
哺乳动物的黑色素生成直接或间接受85多个不同基因座的调控。Tyr/白化病基因座中的突变会导致色素沉着缺失，该基因座编码酪氨酸酶（Tyr），这是黑色素生成的关键限速酶。其他黑色素生成酶包括分别在Tyrp1/棕色和Dct/石板色基因座编码的Tyrp1（或TRP1）和3,4-二羟基苯丙氨酸-铬互变异构酶（Dct或TRP2）。小鼠Tyrp1可以氧化由Dct产生的5,6-二羟基吲哚-2-羧酸（DHICA），但Tyrp1中的突变也会影响Tyr的催化功能。这三种酶都是具有相似结构特征的膜结合黑素小体蛋白，被认为在黑素生成复合物中相互作用并使其稳定。我们现在进一步研究了Tyrp1(b)突变对Tyr稳定性的影响。脉冲/追踪标记实验表明，在该基因座的Tyrp1(b)突变黑素细胞中，Tyr的降解速度比野生型黑素细胞更快。用野生型Tyrp1基因感染可以部分挽救Tyr这种降低的稳定性，同时受感染的黑素细胞的表型也得到挽救。总之，这些结果表明，除了在氧化DHICA中的催化功能外，Tyrp1可能在稳定Tyr方面发挥重要作用，这是其在黑色素形成调控中的第二个潜在作用。
