Department of Molecular Science and Technology, Ajou University, Suwon, Korea.
PLoS One. 2011;6(8):e23989. doi: 10.1371/journal.pone.0023989. Epub 2011 Aug 29.
Toll-like receptors (TLRs) activate a potent immunostimulatory response. There is clear evidence that overactivation of TLRs leads to infectious and inflammatory diseases. Recent biochemical studies have shown that the membrane-bound form of ST2 (ST2L), a member of the Toll-like/IL-1 receptor superfamily, negatively regulates MyD88-dependent TLR signaling pathways by sequestrating the adapters MyD88 and Mal (TIRAP). Specifically, ST2L attenuates the recruitment of Mal and MyD88 adapters to their receptors through its intracellular TIR domain. Thus, ST2L is a potent molecule that acts as a key regulator of endotoxin tolerance and modulates innate immunity. So far, the inhibitory mechanism of ST2L at the molecular level remains elusive. To develop a working hypothesis for the interactions between ST2L, TLRs (TLR1, 2, 4, and 6), and adapter molecules (MyD88 and Mal), we constructed three-dimensional models of the TIR domains of TLR4, 6, Mal, and ST2L based on homology modeling. Since the crystal structures of the TIR domains of TLR1, 2 as well as the NMR solution structure of MyD88 are known, we utilized these structures in our analysis. The TIR domains of TLR1, 2, 4, 6, MyD88, Mal and ST2L were subjected to molecular dynamics (MD) simulations in an explicit solvent environment. The refined structures obtained from the MD simulations were subsequently used in molecular docking studies to probe for potential sites of interactions. Through protein-protein docking analysis, models of the essential complexes involved in TLR2 and 4 signaling and ST2L inhibiting processes were developed. Our results suggest that ST2L may exert its inhibitory effect by blocking the molecular interface of Mal and MyD88 adapters mainly through its BB-loop region. Our predicted oligomeric signaling models may provide a basis for the understanding of the assembly process of TIR domain interactions, which has thus far proven to be difficult via in vivo studies.
Toll 样受体 (TLRs) 激活有效的免疫刺激反应。有明确的证据表明 TLRs 的过度激活会导致感染和炎症性疾病。最近的生化研究表明,Toll-样/IL-1 受体超家族成员 ST2 的膜结合形式 (ST2L) 通过隔离接头分子 MyD88 和 Mal (TIRAP) 负调控 MyD88 依赖性 TLR 信号通路。具体而言,ST2L 通过其胞内 TIR 结构域来减弱 Mal 和 MyD88 接头分子与受体的募集。因此,ST2L 是一种有效的分子,作为内毒素耐受的关键调节剂,并调节先天免疫。到目前为止,ST2L 在分子水平上的抑制机制仍不清楚。为了开发 ST2L、TLRs (TLR1、2、4 和 6) 和接头分子 (MyD88 和 Mal) 之间相互作用的工作假说,我们基于同源建模构建了 TLR4、6、Mal 和 ST2L 的 TIR 结构域的三维模型。由于 TLR1、2 的 TIR 结构域的晶体结构以及 MyD88 的 NMR 溶液结构是已知的,因此我们在分析中利用了这些结构。TLR1、2、4、6、MyD88、Mal 和 ST2L 的 TIR 结构域在明确定溶剂环境下进行分子动力学 (MD) 模拟。从 MD 模拟中获得的细化结构随后用于分子对接研究,以探测潜在的相互作用位点。通过蛋白质-蛋白质对接分析,构建了 TLR2 和 4 信号转导和 ST2L 抑制过程中涉及的必需复合物的模型。我们的结果表明,ST2L 可能通过其 BB-环区域主要阻断 Mal 和 MyD88 接头分子的分子界面来发挥其抑制作用。我们预测的寡聚信号模型可能为理解 TIR 结构域相互作用的组装过程提供基础,迄今为止,通过体内研究证明这一过程非常困难。