Zhang Shikun, Li Bo, Liu Lun, Gong Dongsheng, Zhang Deyu, Liu Fengjiang, Yang Xiuna, Qin Hua, Kong Deling, Zhang Shuyang, Rao Zihe, Cao Xuetao
Department of Immunology, Center for Immunotherapy, Institute of Basic Medical Sciences, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
State Key Laboratory of Medicinal Chemical Biology, Institute of Immunology, College of Life Sciences, Nankai University, Tianjin, China.
Cell Res. 2025 Sep 8. doi: 10.1038/s41422-025-01178-5.
The pre-dimerization of endosome-localized RNA sensor Toll-like receptor 3 (TLR3) is required for its innate recognition, yet how TLR3 pre-dimers are formed and precisely primed for innate activation remains unclear. Here, we demonstrate that endosome-localized self RNA Rmrp directly binds to TLR3 and induces TLR3 dimerization in the early endosome but does not interact with endosome-localized TLR7, TLR8, TLR9 or cytoplasmic RNA sensor RIG-I under homeostatic conditions. Cryo-EM structure of Rmrp-TLR3 complex reveals a novel lapped conformation of TLR3 dimer engaged by Rmrp, which is distinct from the activation mechanism by dsRNA and the specific structural feature at the 3'-end of Rmrp is critical for its functional interaction with TLR3. Furthermore, K42 residue of TLR3 is essential for binding to Rmrp and subsequent dimerization. Rmrp dissociates from TLR3 following endosomal acidification, generating a matured TLR3 dimer which is primed for innate recognition and activation. Myeloid-cell deficiency of Rmrp reduces TLR3 dimerization and attenuates TLR3-mediated antiviral responses against influenza A both in vitro and in vivo. These findings elucidate the structural mode of self RNA Rmrp-primed TLR3 dimerization and ready for efficient innate recognition on endosomal membrane, extending our knowledge of how membrane-associated TLRs pre-dimerize and suggesting a new function of subcellular localized self RNAs in empowering innate activation.
内体定位的RNA传感器Toll样受体3（TLR3）的预二聚化是其天然识别所必需的，然而TLR3预二聚体如何形成以及如何精确地为天然激活做好准备仍不清楚。在这里，我们证明内体定位的自身RNA Rmrp直接与TLR3结合，并在内体早期诱导TLR3二聚化，但在稳态条件下不与内体定位的TLR7、TLR8、TLR9或细胞质RNA传感器RIG-I相互作用。Rmrp-TLR3复合物的冷冻电镜结构揭示了由Rmrp参与的TLR3二聚体的一种新的重叠构象，这与双链RNA的激活机制不同，并且Rmrp 3'端的特定结构特征对于其与TLR3的功能相互作用至关重要。此外，TLR3的K42残基对于与Rmrp结合及随后的二聚化至关重要。内体酸化后，Rmrp从TLR3上解离，产生一个成熟的TLR3二聚体，该二聚体为天然识别和激活做好了准备。Rmrp在髓样细胞中的缺失会减少TLR3二聚化，并在体外和体内减弱TLR3介导的针对甲型流感的抗病毒反应。这些发现阐明了自身RNA Rmrp引发的TLR3二聚化的结构模式，并为在内体膜上进行有效的天然识别做好准备，扩展了我们对膜相关TLR如何预二聚化的认识，并提示了亚细胞定位的自身RNA在增强天然激活方面的新功能。
