Structure of the lysosomal KICSTOR–GATOR1–SAMTOR nutrient-sensing supercomplex; Lupton, Bayly-Jones et al.

The GTP-bound state of the heterodimeric Rag GTPases functions as a molecular switch regulating mTORC1 activation at the lysosome downstream of amino acid fluctuations. Under low amino acid conditions, GATOR1 promotes RagA GTP hydrolysis, preventing mTORC1 activation. KICSTOR recruits and regulates GATOR1 at the lysosome by undefined mechanisms. Here, we resolve the KICSTOR–GATOR1 structure, revealing a striking ~60 nm crescent-shaped assembly. GATOR1 anchors to KICSTOR via an extensive interface, and mutations that disrupt this interaction impair mTORC1 regulation. The S-adenosylmethionine sensor SAMTOR binds KICSTOR in a manner incompatible with metabolite binding, providing structural insight into methionine sensing via SAMTOR–KICSTOR association. We discover that KICSTOR and GATOR1 form a dimeric supercomplex. This assembly restricts GATOR1 to an orientation that favors the low-affinity active GAP mode of Rag GTPase engagement while sterically restricting access to the high-affinity inhibitory mode, consistent with a model of an active lysosomal GATOR1 docking complex.

异二聚体Rag GTP酶（heterodimeric Rag GTPases）的GTP结合态作为分子开关，调控氨基酸波动下游溶酶体处的哺乳动物雷帕霉素靶蛋白复合物1（mTORC1）激活过程。在氨基酸匮乏条件下，GATOR1复合物（GATOR1）可促进RagA的GTP水解，从而阻断mTORC1的激活。KICSTOR复合物（KICSTOR）通过尚未阐明的分子机制，在溶酶体处招募并调控GATOR1。本研究解析了KICSTOR–GATOR1复合物的结构，揭示了一个令人瞩目的约60 nm新月形组装体。GATOR1通过广泛的相互作用界面锚定至KICSTOR，破坏该相互作用的突变会削弱mTORC1的调控功能。S-腺苷甲硫氨酸（S-adenosylmethionine）传感器SAMTOR以与代谢物结合不相容的方式结合KICSTOR，为通过SAMTOR–KICSTOR相互作用实现的甲硫氨酸感知提供了结构层面的机制解析。本研究发现KICSTOR与GATOR1可形成二聚体超级复合物。该组装体将GATOR1限定为有利于Rag GTP酶结合的低亲和力活性GTP酶激活蛋白（GAP）构象，同时空间上阻碍其进入高亲和力抑制性结合模式，这与活性溶酶体GATOR1对接复合物的模型相符。