Department of Medical Protein Research, VIB, B-9000 Ghent, Belgium.
J Cell Sci. 2010 Jan 15;123(Pt 2):256-65. doi: 10.1242/jcs.056002.
Toll-like receptors (TLRs) are crucial components of innate immunity, ensuring efficient responses against invading pathogens. After ligand binding, TLR signaling is initiated by recruitment of adaptor molecules, a step mediated by homotypic Toll-IL-1 receptor (TIR) domain interactions. Four TIR-containing TLR adaptor molecules are described, all of which are susceptible to modification and strict regulation. For example, caspase-1 is reported to cleave the TLR adaptor Mal at position D198, an event that is indispensible for Mal function. In this report, we use the mammalian two-hybrid technique MAPPIT to study the implications of Mal cleavage. We show that a Mal mutant, which mimics caspase-1 cleavage and a caspase-1-uncleavable MalD198A mutant, are abrogated in their bridging function and lose the ability to activate NF-kappaB. A MalD198E mutant is still fully functional, suggesting that caspase-1 cleavage of Mal is not necessary for Mal-mediated signaling. D198 of Mal is conserved in MyD88 and TLR4 TIR domains and the negatively charged amino acid at this position is crucial for the interactions and function of Mal, MyD88 and TLR4 TIR. Our data suggest an inhibitory, rather than an activating role for caspase-1 in Mal regulation, and show that the caspase-1 cleavage site in Mal is part of a TIR-domain interaction site.
toll 样受体 (TLRs) 是先天免疫的关键组成部分，可确保对入侵病原体的有效反应。配体结合后，TLR 信号通过衔接分子的募集而启动，这一步骤由同源 Toll-IL-1 受体 (TIR) 结构域相互作用介导。已经描述了四种含有 TIR 的 TLR 衔接分子，它们都容易受到修饰和严格调控。例如，据报道 caspase-1 在位置 D198 切割 TLR 衔接分子 Mal，这一事件对于 Mal 功能是不可或缺的。在本报告中，我们使用哺乳动物双杂交技术 MAPPIT 研究 Mal 切割的影响。我们表明，模拟 caspase-1 切割的 Mal 突变体和 caspase-1 不可切割的 MalD198A 突变体在桥接功能上被阻断，并且丧失了激活 NF-κB 的能力。MalD198E 突变体仍然具有完全功能，表明 Mal 介导的信号传导不需要 caspase-1 切割 Mal。Mal 的 D198 在 MyD88 和 TLR4 TIR 结构域中保守，该位置的带负电荷的氨基酸对于 Mal、MyD88 和 TLR4 TIR 的相互作用和功能至关重要。我们的数据表明 caspase-1 在 Mal 调节中起抑制作用，而不是激活作用，并表明 Mal 中的 caspase-1 切割位点是 TIR 结构域相互作用位点的一部分。
