Site-one protease (S1P) conducts the first of two cleavage events in the Golgi to activate Sterol regulatory element binding proteins (SREBPs) and upregulate lipogenic transcription. S1P is also required for a wide array of additional signaling pathways. A zymogen serine protease, S1P matures through autoproteolysis of two pro-domains, with one cleavage event in the endoplasmic reticulum (ER) and the other in the Golgi. We recently identified the SREBP regulating gene, (SPRING), which enhances S1P maturation and is necessary for SREBP signaling. Here, we report the cryo-EM structures of S1P and S1P-SPRING at sub-2.5 Å resolution. SPRING activates S1P by dislodging its inhibitory pro-domain and stabilizing intra-domain contacts. Functionally, SPRING licenses S1P to cleave its cognate substrate, SREBP2. Our findings reveal an activation mechanism for S1P and provide insights into how spatial control of S1P activity underpins cholesterol homeostasis.

位点蛋白酶 (S1P) 在高尔基体中进行两个裂解事件中的第一个，以激活甾醇调节元件结合蛋白 (SREBP) 并上调脂肪生成转录。 S1P 也是许多其他信号通路所必需的。 S1P 是一种酶原丝氨酸蛋白酶，通过两个前结构域的自身蛋白水解而成熟，其中一个裂解事件在内质网 (ER) 中，另一个在高尔基体中。我们最近发现了 SREBP 调节基因 (SPRING)，它可以增强 S1P 成熟，并且是 SREBP 信号转导所必需的。在这里，我们报告了 S1P 和 S1P-SPRING 分辨率低于 2.5 Å 的冷冻电镜结构。 SPRING 通过去除其抑制性前结构域并稳定结构域内接触来激活 S1P。从功能上来说，SPRING 授权 S1P 裂解其同源底物 SREBP2。我们的研究结果揭示了 S1P 的激活机制，并为 S1P 活性的空间控制如何支持胆固醇稳态提供了见解。