Modulation of double-stranded RNA recognition by the N-terminal histidine-rich region of the human toll-like receptor 3

Kotaro Fukuda, Tomoya Watanabe, Takashi Tokisue, Tadayuki Tsujita, Satoshi Nishikawa, Tsunemi Hasegawa, Tsukasa Seya, Misako Matsumoto

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

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-stranded RNA (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: His36 in the N-cap region, His60 in LRR1, and His108 in LRR3. Mutagenesis of these residues showed that His39, His60, and His108 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 His39, His60, and His108, 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.

Original languageEnglish
Pages (from-to)22787-22794
Number of pages8
JournalJournal of Biological Chemistry
Volume283
Issue number33
DOIs
Publication statusPublished - 2008 Aug 15

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Fukuda, K., Watanabe, T., Tokisue, T., Tsujita, T., Nishikawa, S., Hasegawa, T., Seya, T., & Matsumoto, M. (2008). Modulation of double-stranded RNA recognition by the N-terminal histidine-rich region of the human toll-like receptor 3. Journal of Biological Chemistry, 283(33), 22787-22794. https://doi.org/10.1074/jbc.M802284200