Structural biology of Toll like receptor/IL 1R signaling

toll样受体（TLRs）和白细胞介素-1受体（IL-lR）超家族成员在宿主抗微生物感染的先天免疫应答中起着至关重要的作用。例如，小鼠TLR4基因的缺失使它们对脂多糖（LPS，也称为内毒素）的反应降低，脂多糖是革兰氏阴性菌独特的细胞壁成分。在哺乳动物和其他脊椎动物中，先天免疫反应对于激活适当的适应性免疫反应也很重要。TLRs和IL-1RS共享一个保守的细胞内结构域，Toll/Interleukin-1 Receptor （TIR）结构域。该结构域的完整性是通过这些受体进行信号转导所必需的。例如，小鼠TLR4的TIR结构域P712H的单点突变导致LPS反应性的消失，与TLR4-/-小鼠的表型相似。其他诱变研究也证实了该结构域在信号传导过程中的重要性。TLRs和IL-1RS的信号通路涉及许多分子，如适配分子MyD88、蛋白激酶IRAK、TRAF6等下游介质。MyD88是一种细胞质蛋白，它也含有一个TIR结构域。最终，信号转导导致转录因子NF-kappaB、应激激酶和AP-1转录因子的激活。TIR结构域被认为是蛋白质-蛋白质相互作用模块。受体被配体结合激活后，通过受体和MyD88适配器分子中存在的TIR结构域形成细胞内信号复合物。这是这些受体信号转导的关键步骤。目前，没有任何关于TIR域的结构信息。该研究项目将填补我们在这些信号转导模块方面的知识空白。这些结构信息将用于了解TLRs和IL-1RS的生物学和生物化学。这些信息还将用于识别可能对信号转导很重要的残基。这些将构成进一步诱变、生化和功能研究的基础，以评估其重要性。

Toll-like receptors (TLRs) and members of the interleukin-1 receptor (IL-lR) superfamily have crucial roles in host innate immune response against microbial infections. For example, deletion of the TLR4 gene in mice renders them hyporesponsive to lipopolysaccharide (LPS, also known as endotoxin), which is a unique cell-wall component of Gram-negative bacteria. In mammals and other vertebrates, the innate immune response is also important for the activation of the proper adaptive immune response. The TLRs and the IL-1RS share a conserved intra-cellular domain, the Toll/Interleukin-1 Receptor (TIR) domain. The integrity of this domain is required for the signal transduction through these receptors. For example, a single-point mutation in the TIR domain of murine TLR4, P712H, leads to the abrogation of LPS responsiveness, similar to the phenotype of the TLR4-/- mice. Additional mutagenesis studies also confirm the importance of this domain in the signaling process. The signaling pathway of the TLRs and IL-1RS involves many molecules, such as the adapter molecule MyD88, the protein kinase IRAK, TRAF6, and other down-stream mediators. MyD88 is a cytoplasmic protein and it also contains a TIR domain. Ultimately, the signal transduction leads to the activation of the transcription factor NF-kappaB, the stress kinases and the AP-1 transcription factors. TIR domains are believed to be protein-protein interaction modules. Upon receptor activation by ligand binding, an intra-cellular signaling complex is formed via the TIR domains that are present in the receptors and the MyD88 adapter molecule. This is a crucial step in the signal transduction by these receptors. Currently, there is no structural information on any of the TIR domains. The proposed research project will fill this gap in our knowledge on these signal transduction modules. The structural information will be used to understand the biology and biochemistry of the TLRs and the IL-1RS. The information will also be used to identify residues that may be important for the signal transduction. These will form the basis for further mutagenesis, biochemical, and functional studies to assess their importance.