Fig4 is a phosphoinositide phosphatase that converts PI3,5P2 to PI3P. Paradoxically, mutation of Fig4 results in lower PI3,5P2, indicating that Fig4 is also required for PI3,5P2 production. Fig4 promotes elevation of PI3,5P2, in part, through stabilization of a protein complex that includes its opposing lipid kinase, Fab1, and the scaffold protein Vac14. Here we show that multiple regions of Fig4 contribute to its roles in the elevation of PI3,5P2: its catalytic site, an N-terminal disease-related surface, and a C-terminal region. We show that mutation of the Fig4 catalytic site enhances the formation of the Fab1-Vac14-Fig4 complex, and reduces the ability to elevate PI3,5P2. This suggests that independent of its lipid phosphatase function, the active site plays a role in the Fab1-Vac14-Fig4 complex. We also show that the N-terminal disease-related surface contributes to the elevation of PI3,5P2 and promotes Fig4 association with Vac14 in a manner that requires the Fig4 C-terminus. We find that the Fig4 C-terminus alone interacts with Vac14 in vivo and retains some functions of full-length Fig4. Thus, a subset of Fig4 functions are independent of its phosphatase domain and at least three regions of Fig4 play roles in the function of the Fab1-Vac14-Fig4 complex.

中文翻译：

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脂质磷酸酶在激活其相反脂质激酶中的作用。

Fig4 是一种将 PI3、5P2 转化为 PI3P 的磷酸肌醇磷酸酶。矛盾的是，Fig4 的突变导致较低的 PI3,5P2，表明 Fig4 也是 PI3,5P2 生产所必需的。Fig4 促进 PI3、5P2 的升高，部分原因是通过稳定蛋白质复合物，该复合物包括其相反的脂质激酶 Fab1 和支架蛋白 Vac14。在这里，我们显示 Fig4 的多个区域有助于其在 PI3,5P2 升高中的作用：其催化位点、N 端疾病相关表面和 C 端区域。我们表明 Fig4 催化位点的突变增强了 Fab1-Vac14-Fig4 复合物的形成，并降低了提升 PI3、5P2 的能力。这表明，独立于其脂质磷酸酶功能，活性位点在 Fab1-Vac14-Fig4 复合物中起作用。我们还表明 N 端疾病相关表面有助于 PI3、5P2 的升高，并以需要 Fig4 C 端的方式促进 Fig4 与 Vac14 的关联。我们发现 Fig4 C 端单独在体内与 Vac14 相互作用并保留了全长 Fig4 的一些功能。因此，Fig4 功能的一个子集独立于其磷酸酶结构域，并且 Fig4 的至少三个区域在 Fab1-Vac14-Fig4 复合物的功能中起作用。