Department of Physiology, The Johns Hopkins University, Baltimore, MD 21205, USA.
Proc Natl Acad Sci U S A. 2011 Mar 29;108(13):5390-5. doi: 10.1073/pnas.1014959108. Epub 2011 Mar 15.
In human disorders, the genotype-phenotype relationships are often complex and influenced by genetic and/or environmental factors. Wilson disease (WD) is a monogenic disorder caused by mutations in the copper-transporting P-type ATPase ATP7B. WD shows significant phenotypic diversity even in patients carrying identical mutations; the basis for such diverse manifestations is unknown. We demonstrate that the 2623A/G polymorphism (producing the Gly(875) → Arg substitution in the A-domain of ATP7B) drastically alters the intracellular properties of ATP7B, whereas copper reverses the effects. Under basal conditions, the common Gly(875) variant of ATP7B is targeted to the trans-Golgi network (TGN) and transports copper into the TGN lumen. In contrast, the Arg(875) variant is located in the endoplasmic reticulum (ER) and does not deliver copper to the TGN. Elevated copper corrects the ATP7B-Arg(875) phenotype. Addition of only 0.5-5 μM copper triggers the exit of ATP7B-Arg(875) from the ER and restores copper delivery to the TGN. Analysis of the recombinant A-domains by NMR suggests that the ER retention of ATP7B-Arg(875) is attributable to increased unfolding of the Arg(875)-containing A-domain. Copper is not required for the folding of ATP7B-Arg(875) during biosynthesis, but it stabilizes protein and stimulates its activity. A chemotherapeutical drug, cisplatin, that mimics a copper-bound state of ATP7B also corrects the "disease-like" phenotype of ATP7B-Arg(875) and promotes its TGN targeting and transport function. We conclude that in populations harboring the Arg(875) polymorphism, the levels of bioavailable copper may play a vital role in the manifestations of WD.
在人类疾病中，基因型-表型关系通常较为复杂，并受到遗传和/或环境因素的影响。Wilson 病（WD）是一种由铜转运 P 型 ATP 酶 ATP7B 基因突变引起的单基因疾病。WD 即使在携带相同突变的患者中也表现出显著的表型多样性；这种多样表现的基础尚不清楚。我们证明 2623A/G 多态性（导致 ATP7B 的 A 结构域中 Gly(875)→Arg 取代）极大地改变了 ATP7B 的细胞内特性，而铜则逆转了这种作用。在基础条件下，ATP7B 的常见 Gly(875)变体靶向反式高尔基体网络（TGN）并将铜运入 TGN 腔。相比之下，Arg(875)变体位于内质网（ER）中，不会将铜递送至 TGN。升高的铜纠正了 ATP7B-Arg(875)表型。仅添加 0.5-5 μM 铜就会触发 ATP7B-Arg(875)从 ER 中逸出，并恢复铜向 TGN 的递运。通过 NMR 对重组 A 结构域的分析表明，ATP7B-Arg(875)的 ER 保留归因于 Arg(875)包含的 A 结构域的展开增加。铜不是 ATP7B-Arg(875)在生物合成过程中折叠所必需的，但它稳定了蛋白质并刺激了其活性。一种模拟 ATP7B 结合铜状态的化疗药物顺铂也纠正了 ATP7B-Arg(875)的“疾病样”表型，并促进其 TGN 靶向和运输功能。我们得出结论，在携带 Arg(875)多态性的人群中，生物可利用铜的水平可能在 WD 的表现中起着至关重要的作用。
