Modulation of double-stranded RNA recognition by the N-terminal histidine-rich region of the human toll-like receptor
Modulation of double-stranded RNA recognition by the N-terminal histidine-rich region of the human toll-like receptor
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DOI：
10.1074/jbc.m802284200
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发表时间：
2008-08-15
影响因子：
4.8
通讯作者：
Matsumoto, Misako
中科院分区：
文献类型：
--
作者：
Fukuda, Kotaro;Watanabe, Tomoya;Matsumoto, Misako
Toll样受体（TLR）是对微生物病原体的先天免疫应答的重要组成部分。TLR 3定位于细胞内区室，如内体，并响应病毒来源的双链RNA（dsRNA）启动信号。参与dsRNA识别的TLR 3胞外域（ECD）是由23个富含亮氨酸的重复序列（LRR）组成的马蹄形螺线管。最近对TLR 3 ECD的诱变研究表明，TLR 3的激活依赖于C-末端区域非糖基化表面上的单个结合位点，包括H539和LRR 17至-20内的几个天冬酰胺。TLR 3定位在内体中是配体识别所必需的，这表明酸性pH是TLR 3配体结合的驱动力。为了在结构水平上阐明TLR 3的pH依赖性结合机制，我们集中于聚集在TLR 3 ECD的N-末端区域的三个高度保守的组氨酸残基：N-帽区域中的His（39）、LRR 1中的His（60）和LRR 3中的His（108）。这些残基的诱变显示His（39）、His（60）和His（108）对于基于细胞的测定中的配体依赖性TLR 3活化是必需的。此外，dsRNA与重组TLR 3 ECD的结合强烈依赖于pH和dsRNA长度，并且通过His（39）、His（60）和His（108）的突变而降低，表明TLR 3信号传导通过pH依赖性结合机制从内体起始，并且第二dsRNA结合位点存在于TLR 3 ECD特征螺线管的N末端区域中。我们提出了一种新的模型，形成TLR 3 ECD二聚体与dsRNA复合，其中包括这第二个结合位点。
Toll- like receptors (TLRs) are an essential component of the innate immune response to microbial pathogens. TLR3 is localized in intracellular compartments, such as endosomes, and initiates signals in response to virus- derived double-strandedRNA (dsRNA). The TLR3 ectodomain (ECD), which is implicated in dsRNA recognition, is a horseshoe-shaped solenoid composed of 23 leucine- rich repeats (LRRs). Recent mutagenesis studies on the TLR3 ECD revealed that TLR3 activation depends on a single binding site on the nonglycosylated surface in the C-terminal region, comprising H539 and several asparagines within LRR17 to -20. TLR3 localization within endosomes is required for ligand recognition, suggesting that acidic pH is the driving force for TLR3 ligand binding. To elucidate the pH- dependent binding mechanism of TLR3 at the structural level, we focused on three highly conserved histidine residues clustered at the N-terminal region of the TLR3 ECD: His(39) in the N-cap region, His(60) in LRR1, and His(108) in LRR3. Mutagenesis of these residues showed that His(39), His(60), and His(108) were essential for ligand-dependent TLR3 activation in a cell- based assay. Furthermore, dsRNA binding to recombinant TLR3 ECD depended strongly on pH and dsRNA length and was reduced by mutation of His(39), His(60), and His(108), demonstrating that TLR3 signaling is initiated from the endosome through a pH- dependent binding mechanism, and that a second dsRNA binding site exists in the N-terminal region of the TLR3 ECD characteristic solenoid. We propose a novel model for the formation of TLR3 ECD dimers complexed with dsRNA, which incorporates this second binding site.