Manik Mohammad K, Pan Mengqi, Xiao Le, Gu Weixi, Kim Hyoyoung, Pospich Sabrina, Hedger Andrew, Vajjhala Parimala R, Lee Morris Y L, Qian Xiaoqi, Landsberg Michael J, Ve Thomas, Nanson Jeffrey D, Raunser Stefan, Stacey Katryn J, Wu Hao, Kobe Bostjan
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA 02115.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2418988122. doi: 10.1073/pnas.2418988122. Epub 2025 Jan 9.
Innate immunity relies on Toll-like receptors (TLRs) to detect pathogen-associated molecular patterns. The TIR (Toll/interleukin-1 receptor) domain-containing TLR adaptors TRIF (TIR domain-containing adaptor-inducing interferon-β) and TRAM (TRIF-related adaptor molecule) are essential for MyD88-independent TLR signaling. However, the structural basis of TRIF and TRAM TIR domain-based signaling remains unclear. Here, we present cryo-EM structures of filaments formed by TRIF and TRAM TIR domains at resolutions of 3.3 Å and 5.6 Å, respectively. Both structures reveal two-stranded parallel helical arrangements. Functional studies underscore the importance of intrastrand interactions, mediated by the BB-loop, and interstrand interactions in TLR4-mediated signaling. We also report the crystal structure of the monomeric TRAM TIR domain bearing the BB loop mutation C117H, which reveals conformational differences consistent with its inactivity. Our findings suggest a unified signaling mechanism by the TIR domains of the four signaling TLR adaptors MyD88, MAL, TRIF, and TRAM and reveal potential therapeutic targets for immunity-related disorders.
固有免疫依赖于Toll样受体（TLR）来检测病原体相关分子模式。含TIR（Toll/白细胞介素-1受体）结构域的TLR衔接蛋白TRIF（含TIR结构域的衔接蛋白诱导干扰素-β）和TRAM（TRIF相关衔接分子）对于不依赖MyD88的TLR信号传导至关重要。然而，基于TRIF和TRAM TIR结构域的信号传导的结构基础仍不清楚。在此，我们分别以3.3 Å和5.6 Å的分辨率展示了由TRIF和TRAM TIR结构域形成的细丝的冷冻电镜结构。两种结构均揭示了双链平行螺旋排列。功能研究强调了由BB环介导的链内相互作用以及TLR4介导的信号传导中的链间相互作用的重要性。我们还报道了携带BB环突变C117H的单体TRAM TIR结构域的晶体结构，该结构揭示了与其无活性一致的构象差异。我们的研究结果表明了四种信号传导TLR衔接蛋白MyD88、MAL、TRIF和TRAM的TIR结构域的统一信号传导机制，并揭示了免疫相关疾病的潜在治疗靶点。
