Westlake Laboratory of Life Sciences and Biomedicine, Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou 310024, Zhejiang Province, China.
Institute of Biology, Westlake Institute for Advanced Study, Hangzhou 310024, Zhejiang Province, China.
Science. 2021 Mar 5;371(6533). doi: 10.1126/science.abb2224. Epub 2021 Jan 14.
The sterol regulatory element-binding protein (SREBP) pathway controls cellular homeostasis of sterols. The key players in this pathway, Scap and Insig-1 and -2, are membrane-embedded sterol sensors. The 25-hydroxycholesterol (25HC)-dependent association of Scap and Insig acts as the master switch for the SREBP pathway. Here, we present cryo-electron microscopy analysis of the human Scap and Insig-2 complex in the presence of 25HC, with the transmembrane (TM) domains determined at an average resolution of 3.7 angstrom. The sterol-sensing domain in Scap and all six TMs in Insig-2 were resolved. A 25HC molecule is sandwiched between the S4 to S6 segments in Scap and TMs 3 and 4 in Insig-2 in the luminal leaflet of the membrane. Unwinding of the middle of the Scap-S4 segment is crucial for 25HC binding and Insig association.
固醇调节元件结合蛋白（SREBP）途径控制固醇的细胞内稳态。该途径中的关键参与者 Scap 和 Insig-1 和 -2 是膜嵌入的固醇传感器。Scap 和 Insig 的 25-羟胆固醇（25HC）依赖性结合充当 SREBP 途径的主开关。在这里，我们呈现了在存在 25HC 时人源 Scap 和 Insig-2 复合物的低温电子显微镜分析，跨膜（TM）结构域的平均分辨率为 3.7 埃。在 Scap 中的固醇感应结构域和 Insig-2 中的所有六个 TM 都被解析出来。在膜的腔侧叶中，一个 25HC 分子夹在 Scap 的 S4 到 S6 片段之间和 Insig-2 的 TM3 和 TM4 之间。Scap-S4 片段的中间部分的展开对于 25HC 结合和 Insig 结合至关重要。
