Department of Physiology, Johns Hopkins University, Baltimore, Maryland 21205, USA.
J Biol Chem. 2012 Oct 19;287(43):36041-50. doi: 10.1074/jbc.M112.370403. Epub 2012 Aug 16.
The copper-transporting ATPase ATP7B has a dual intracellular localization: the trans-Golgi network (TGN) and cytosolic vesicles. Changes in copper levels, kinase-mediated phosphorylation, and mutations associated with Wilson disease alter the steady-state distribution of ATP7B between these compartments. To identify a primary molecular event that triggers ATP7B exit from the TGN, we characterized the folding, activity, and trafficking of the ATP7B variants with mutations within the regulatory N-terminal domain (N-ATP7B). We found that structural changes disrupting the inter-domain contacts facilitate ATP7B exit from the TGN. Mutating Ser-340/341 in the N-ATP7B individually or together to Ala, Gly, Thr, or Asp produced active protein and shifted the steady-state localization of ATP7B to vesicles, independently of copper levels. The Ser340/341G mutant had a lower kinase-mediated phosphorylation under basal conditions and no copper-dependent phosphorylation. Thus, negative charges introduced by copper-dependent phosphorylation are not obligatory for ATP7B trafficking from the TGN. The Ser340/341A mutation did not alter the overall fold of N-ATP7B, but significantly decreased interactions with the nucleotide-binding domain, mimicking consequences of copper binding to N-ATP7B. We propose that structural changes that specifically alter the inter-domain contacts initiate exit of ATP7B from the TGN, whereas increased phosphorylation may be needed to maintain an open interface between the domains.
铜转运 ATP 酶 ATP7B 具有双重细胞内定位:高尔基体中转体(TGN)和胞质小泡。铜水平的变化、激酶介导的磷酸化以及与威尔逊病相关的突变改变了 ATP7B 在这些隔室之间的稳态分布。为了确定触发 ATP7B 从 TGN 中逸出的主要分子事件,我们对具有调节 N 端结构域(N-ATP7B)内突变的 ATP7B 变体的折叠、活性和运输进行了表征。我们发现,破坏结构域间接触的结构变化促进了 ATP7B 从 TGN 逸出。在 N-ATP7B 中单独或一起将丝氨酸 340/341 突变为丙氨酸、甘氨酸、苏氨酸或天冬氨酸会产生活性蛋白,并将 ATP7B 的稳态定位独立于铜水平转移到小泡中。Ser340/341G 突变体在基础条件下具有较低的激酶介导的磷酸化作用,且无铜依赖性磷酸化作用。因此,铜依赖性磷酸化作用引入的负电荷对于 ATP7B 从 TGN 的运输不是必需的。Ser340/341A 突变并未改变 N-ATP7B 的整体折叠,但显著降低了与核苷酸结合结构域的相互作用,模拟了铜与 N-ATP7B 结合的后果。我们提出,特异性改变结构域间接触的结构变化启动了 ATP7B 从 TGN 中的逸出,而增加的磷酸化作用可能需要维持结构域之间的开放界面。