Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Review Article
  • Published:

Assembly and localization of Toll-like receptor signalling complexes

Nature Reviews Immunology volume 14, pages 546–558 (2014)Cite this article

Subjects

Key Points

  • The Toll-like receptors (TLRs) respond to pathogen-associated molecular patterns (PAMPs), which include bacterial lipids and non-self nucleic acids. Structural studies have identified three distinct modes of TLR activation: ligand-induced dimerization, ligand-induced rearrangement of a preformed dimer and receptor homodimerization that is induced indirectly by ligand binding.

  • TLR activation causes a conformational rearrangement of the receptor transmembrane and juxtamembrane sequences, which leads to the association of the cytosolic Toll/IL-1R (TIR) domains of the receptor.

  • Multiple types of post-receptor complexes are formed by interactions between receptor and adaptor protein TIR domains. Bitypic TIR domain–TIR domain interactions are weak but cooperative assembly leads to a stable signalling scaffold.

  • Higher-order scaffolds are generated by helical polymerization of the death domains of myeloid differentiation primary response protein 88 (MYD88) and IL-1R-associated kinases (IRAKs). The 'Myddosome' has a hierarchical arrangement of subunits that assemble in a process that displays positive cooperativity.

  • TLR signalling pathways are also regulated at the level of cell biology. Biosynthesis and anterograde trafficking from the endoplasmic reticulum to the cell surface and endosomal compartments is coupled to endocytosis and downregulation in the endolysosomal pathway.

  • Specialized membrane microdomains or lipid rafts may have important roles in the formation of signalling scaffolds.

Abstract

Signal transduction by the Toll-like receptors (TLRs) is central to host defence against many pathogenic microorganisms and also underlies a large burden of human disease. Thus, the mechanisms and regulation of signalling by TLRs are of considerable interest. In this Review, we discuss the molecular basis for the recognition of pathogen-associated molecular patterns, the nature of the protein complexes that mediate signalling, and the way in which signals are regulated and integrated at the level of allosteric assembly, post-translational modification and subcellular trafficking of the components of the signalling complexes. These fundamental molecular mechanisms determine whether the signalling output leads to a protective immune response or to serious pathologies such as sepsis. A detailed understanding of these processes at the molecular level provides a rational framework for the development of new drugs that can specifically target pathological rather than protective signalling in inflammatory and autoimmune disease.

Access through your institution
Buy or subscribe

This is a preview of subscription content, access via your institution

Access options

Access through your institution

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Overview of TLR signalling pathways.
Figure 2: Ligand recognition and signal transduction.
Figure 3: Interactions underlying signalling through TIR domain-containing complexes.
Figure 4: Death domain interactions position protein kinases in the Myddosome assembly.
Figure 5: Chaperones and pathways in the cellular trafficking of TLRs.

Similar content being viewed by others

References

  1. Janeway, C. A. Jr. Approaching the asymptote? Evolution and revolution in immunology. Cold Spring Harb. Symp. Quant. Biol. 54, 1–13 (1989).

    Article  CAS  PubMed  Google Scholar 

  2. Gay, N. J. & Gangloff, M. Structure and function of Toll receptors and their ligands. Annu. Rev. Biochem. 76, 141–165 (2007).

    Article  CAS  PubMed  Google Scholar 

  3. Kang, J. Y. et al. Recognition of lipopeptide patterns by Toll-like receptor 2-Toll-like receptor 6 heterodimer. Immunity 31, 873–884 (2009).

    Article  CAS  PubMed  Google Scholar 

  4. Jin, M. S. et al. Crystal structure of the TLR1-TLR2 heterodimer induced by binding of a tri-acylated lipopeptide. Cell 130, 1071–1082 (2007).

    Article  CAS  PubMed  Google Scholar 

  5. Yoon, S. I. et al. Structural basis of TLR5-flagellin recognition and signaling. Science 335, 859–864 (2012).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Shimazu, R. et al. MD-2, a molecule that confers lipopolysaccharide responsiveness on Toll-like receptor 4. J. Exp. Med. 189, 1777–1782 (1999).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Ohto, U., Fukase, K., Miyake, K. & Satow, Y. Crystal structures of human MD-2 and its complex with antiendotoxic lipid IVa. Science 316, 1632–1634 (2007).

    Article  CAS  PubMed  Google Scholar 

  8. Kim, H. M. et al. Crystal structure of the TLR4-MD-2 complex with bound endotoxin antagonist Eritoran. Cell 130, 906–917 (2007).

    Article  CAS  PubMed  Google Scholar 

  9. Park, B. S. et al. The structural basis of lipopolysaccharide recognition by the TLR4–MD-2 complex. Nature 458, 1191–1195 (2009). This paper describes the crystal structure of a TLR4–MD2 heterotetramer bound to agonistic hexa-acyl LPS.

    Article  CAS  PubMed  Google Scholar 

  10. Hemmi, H. et al. Small anti-viral compounds activate immune cells via the TLR7 MyD88-dependent signaling pathway. Nature Immunol. 3, 196–200 (2002).

    Article  CAS  Google Scholar 

  11. Tanji, H., Ohto, U., Shibata, T., Miyake, K. & Shimizu, T. Structural reorganization of the Toll-like receptor 8 dimer induced by agonistic ligands. Science 339, 1426–1429 (2013). This study solves the structure of TLR8 dimers both in an inactive form and bound to small-molecule agonists. This shows how small molecules can induce large conformational changes in TLR ectodomains.

    Article  CAS  PubMed  Google Scholar 

  12. Latz, E. et al. Ligand-induced conformational changes allosterically activate Toll-like receptor 9. Nature Immunol. 8, 772–779 (2007).

    Article  CAS  Google Scholar 

  13. Gibbard, R. J., Morley, P. J. & Gay, N. J. Conserved features in the extracellular domain of human Toll-like receptor 8 are essential for pH-dependent signaling. J. Biol. Chem. 281, 27503–27511 (2006).

    Article  CAS  PubMed  Google Scholar 

  14. Rutz, M. et al. Toll-like receptor 9 binds single-stranded CpG-DNA in a sequence- and pH-dependent manner. Eur. J. Immunol. 34, 2541–2550 (2004).

    Article  CAS  PubMed  Google Scholar 

  15. Nikolova, E. N., Goh, G. B., Brooks, C. L. 3rd & Al-Hashimi, H. M. Characterizing the protonation state of cytosine in transient G.C Hoogsteen base pairs duplex DNA. J. Amer. Chem. Soc. 135, 6766–6769 (2013).

    Article  CAS  Google Scholar 

  16. Gantier, M. P. et al. Rational design of immunostimulatory siRNAs. Mol. Therap. 18, 785–795 (2010).

    Article  CAS  Google Scholar 

  17. Ewald, S. E. et al. Nucleic acid recognition by Toll-like receptors is coupled to stepwise processing by cathepsins and asparagine endopeptidase. J. Exp. Med. 208, 643–651 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  18. Ewald, S. E. et al. The ectodomain of Toll-like receptor 9 is cleaved to generate a functional receptor. Nature 456, 658–662 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  19. Park, B. et al. Proteolytic cleavage in an endolysosomal compartment is required for activation of Toll-like receptor 9. Nature Immunol. 9, 1407–1414 (2008).

    Article  CAS  Google Scholar 

  20. Liu, L. et al. Structural basis of Toll-like receptor 3 signaling with double-stranded RNA. Science 320, 379–381 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  21. Luo, J. et al. Lateral clustering of TLR3:dsRNA signaling units revealed by TLR3ecd:3Fabs quaternary structure. J. Mol. Biol. 421, 112–124 (2012).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  22. Lewis, M. et al. Cytokine Spatzle binds to the Drosophila immunoreceptor Toll with a neurotrophin-like specificity and couples receptor activation. Proc. Natl Acad. Sci. USA 110, 20461–20466 (2013). This paper shows that the binding of D. melanogaster Toll to its ligand Spätzle is markedly different to the binding of TLRs to their ligands and, instead, is similar to vertebrate neurotrophin–neurotrophin receptor complexes.

    Article  CAS  PubMed  Google Scholar 

  23. Gangloff, M. et al. Structural insight into the mechanism of activation of the Toll receptor by the dimeric ligand Spatzle. J. Biol. Chem. 283, 14629–14635 (2008).

    Article  CAS  PubMed  Google Scholar 

  24. Gay, N. J. & Gangloff, M. in Toll-Like Receptors (TLRs) and Innate Immunity (eds Bauer, S. & Hartmann, G.) 181–200 (Springer-Verlag, 2008).

    Book  Google Scholar 

  25. Panter, G. & Jerala, R. The ectodomain of the Toll-like receptor 4 prevents constitutive receptor activation. J. Biol. Chem. 286, 23334–23344 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  26. Endres, N. F. et al. Conformational coupling across the plasma membrane in activation of the EGF receptor. Cell 152, 543–556 (2013). This study reveals the conformational changes that occur in the transmembrane and juxtamembrane sequences of the EGFR following activation — a model for TLR activation.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  27. O'Neill, L. A. & Bowie, A. G. The family of five: TIR-domain-containing adaptors in Toll-like receptor signalling. Nature Rev. Immunol. 7, 353–364 (2007).

    Article  CAS  Google Scholar 

  28. Snyder, G. A. et al. Crystal structures of the Toll/Interleukin-1 receptor (TIR) domains from the Brucella protein TcpB and host adaptor TIRAP reveal mechanisms of molecular mimicry. J. Biol. Chem. 289, 669–679 (2014).

    Article  CAS  PubMed  Google Scholar 

  29. Xu, Y. W. et al. Structural basis for signal transduction by the Toll/interleukin-1 receptor domains. Nature 408, 111–115 (2000).

    Article  CAS  PubMed  Google Scholar 

  30. Nyman, T. et al. The crystal structure of the human Toll-like receptor 10 cytoplasmic domain reveals a putative signaling dimer. J. Biol. Chem. 283, 11861–11865 (2008).

    Article  CAS  PubMed  Google Scholar 

  31. Valkov, E. et al. Crystal structure of Toll-like receptor adaptor MAL/TIRAP reveals the molecular basis for signal transduction and disease protection. Proc. Natl Acad. Sci. USA 108, 14879–14884 (2011).

    Article  PubMed  Google Scholar 

  32. Ohnishi, H. et al. Structural basis for the multiple interactions of the MyD88 TIR domain in TLR4 signaling. Proc. Natl Acad. Sci. USA 106, 10260–10265 (2009).

    Article  PubMed  Google Scholar 

  33. Enokizono, Y. et al. Structures and interface mapping of the TIR domain-containing adaptor molecules involved in interferon signaling. Proc. Natl Acad. Sci. USA 110, 19908–19913 (2013).

    Article  CAS  PubMed  Google Scholar 

  34. Poltorak, A. et al. Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene. Science 282, 2085–2088 (1998).

    Article  CAS  PubMed  Google Scholar 

  35. Funami, K. et al. Spatiotemporal mobilization of Toll/IL-1 receptor domain-containing adaptor molecule-1 in response to dsRNA. J. Immunol. 179, 6867–6872 (2007).

    Article  CAS  PubMed  Google Scholar 

  36. Nishiya, T., Kajita, E., Horinouchi, T., Nishimoto, A. & Miwa, S. Distinct roles of TIR and non-TIR regions in the subcellular localization and signaling properties of MyD88. FEBS Lett. 581, 3223–3229 (2007).

    Article  CAS  PubMed  Google Scholar 

  37. Kagan, J. C. & Medzhitov, R. Phosphoinositide-mediated adaptor recruitment controls Toll-like receptor signaling. Cell 125, 943–955 (2006).

    Article  CAS  PubMed  Google Scholar 

  38. Rowe, D. C. et al. The myristoylation of TRIF-related adaptor molecule is essential for Toll-like receptor 4 signal transduction. Proc. Natl Acad. Sci. USA 103, 6299–6304 (2006).

    Article  CAS  PubMed  Google Scholar 

  39. McGettrick, A. F. et al. Trif-related adapter molecule is phosphorylated by PKCɛ during Toll-like receptor 4 signaling. Proc. Natl Acad. Sci. USA 103, 9196–9201 (2006).

    Article  CAS  PubMed  Google Scholar 

  40. Nunez Miguel, R. et al. A dimer of the Toll-like receptor 4 cytoplasmic domain provides a specific scaffold for the recruitment of signalling adaptor proteins. PLoS ONE 2, e788 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  41. Toshchakov, V. Y., Fenton, M. J. & Vogel, S. N. Cutting Edge: differential inhibition of TLR signaling pathways by cell-permeable peptides representing BB loops of TLRs. J. Immunol. 178, 2655–2660 (2007).

    Article  CAS  PubMed  Google Scholar 

  42. Matsunaga, N., Tsuchimori, N., Matsumoto, T. & Ii, M. TAK-242 (Resatorvid), a small-molecule inhibitor of Toll-like receptor (TLR) 4 signaling, binds selectively to TLR4 and interferes with interactions between TLR4 and its adaptor molecules. Mol. Pharmacol. 79, 34–41 (2011).

    Article  CAS  PubMed  Google Scholar 

  43. Gangloff, M. Different dimerisation mode for TLR4 upon endosomal acidification? Trends Biochem. Sci. 37, 92–98 (2012).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  44. Khor, C. C. et al. A Mal functional variant is associated with protection against invasive pneumococcal disease, bacteremia, malaria and tuberculosis. Nature Genet. 39, 523–528 (2007).

    Article  CAS  PubMed  Google Scholar 

  45. Zhang, Y. X. et al. Association of TIRAP (MAL) gene polymorhisms with susceptibility to tuberculosis in a Chinese population. Genet. Mol. Res. 10, 7–15 (2011).

    Article  CAS  PubMed  Google Scholar 

  46. von Bernuth, H. et al. Pyogenic bacterial infections in humans with MyD88 deficiency. Science 321, 691–696 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  47. Jiang, Z. et al. Details of Toll-like receptor:adapter interaction revealed by germ-line mutagenesis. Proc. Natl Acad. Sci. USA 103, 10961–10966 (2006).

    Article  CAS  PubMed  Google Scholar 

  48. Toshchakov, V. Y., Szmacinski, H., Couture, L. A., Lakowicz, J. R. & Vogel, S. N. Targeting TLR4 signaling by TLR4 Toll/IL-1 receptor domain-derived decoy peptides: identification of the TLR4 Toll/IL-1 receptor domain dimerization interface. J. Immunol. 186, 4819–4827 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  49. Piao, W. et al. Recruitment of TLR adapter TRIF to TLR4 signaling complex is mediated by the second helical region of TRIF TIR domain. Proc. Natl Acad. Sci. USA 110, 19036–19041 (2013).

    Article  CAS  PubMed  Google Scholar 

  50. Verstak, B., Arnot, C. J. & Gay, N. J. An alanine-to-proline mutation in the BB-loop of TLR3 Toll/IL-1R domain switches signalling adaptor specificity from TRIF to MyD88. J. Immunol. 191, 6101–6109 (2013).

    Article  CAS  PubMed  Google Scholar 

  51. Leonard, J. N. et al. The TLR3 signaling complex forms by cooperative receptor dimerization. Proc. Natl Acad. Sci. USA 105, 258–263 (2008).

    Article  PubMed  Google Scholar 

  52. Motshwene, P. G. et al. An oligomeric signaling platform formed by the Toll-like receptor signal transducers MyD88 and IRAK-4. J. Biol. Chem. 284, 25404–25411 (2009). This study describes for the first time the composition of the Myddosome and provides evidence for the importance of lipid rafts in TLR signalling.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  53. Gay, N. J., Gangloff, M. & Weber, A. N. Toll-like receptors as molecular switches. Nature Rev. Immunol. 6, 693–698 (2006).

    Article  CAS  Google Scholar 

  54. Ferrao, R. & Wu, H. Helical assembly in the death domain (DD) superfamily. Curr. Opin. Str. Biol. 22, 241–247 (2012).

    Article  CAS  Google Scholar 

  55. Flannery, S. & Bowie, A. G. The interleukin-1 receptor-associated kinases: critical regulators of innate immune signalling. Bioch. Pharmacol. 80, 1981–1991 (2010).

    Article  CAS  Google Scholar 

  56. Burns, K. et al. MyD88, an adapter protein involved in interleukin-1 signaling. J. Biol. Chem. 273, 12203–12209 (1998).

    Article  CAS  PubMed  Google Scholar 

  57. Gay, N. J., Gangloff, M. & O'Neill, L. A. What the Myddosome structure tells us about the initiation of innate immunity. Trends Immunol. 32, 104–109 (2011).

    Article  CAS  PubMed  Google Scholar 

  58. Lin, S. C., Lo, Y. C. & Wu, H. Helical assembly in the MyD88-IRAK4-IRAK2 complex in TLR/IL-1R signalling. Nature 465, 885–890 (2010). This study elucidates the structure of a variant Myddosome consisting of six MYD88 molecules, four IRAK4 molecules and four IRAK2 molecules arranged in a helical, hierarchical complex.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  59. Popovych, N., Sun, S., Ebright, R. H. & Kalodimos, C. G. Dynamically driven protein allostery. Nature Struct. Mol. Biol. 13, 831–838 (2006).

    Article  CAS  Google Scholar 

  60. Burns, K. et al. Inhibition of interleukin 1 receptor/Toll-like receptor signaling through the alternatively spliced, short form of MyD88 is due to its failure to recruit IRAK-4. J. Exp. Med. 197, 263–268 (2003).

    Article  PubMed  PubMed Central  Google Scholar 

  61. Avbelj, M., Horvat, S. & Jerala, R. The role of intermediary domain of MyD88 in cell activation and therapeutic inhibition of TLRs. J. Immunol. 187, 2394–2404 (2011).

    Article  CAS  PubMed  Google Scholar 

  62. George, J. et al. Two human MYD88 variants, S34Y and R98C, interfere with MyD88-IRAK4-myddosome assembly. J. Biol. Chem. 286, 1341–1353 (2011).

    Article  CAS  PubMed  Google Scholar 

  63. Zhou, H. et al. IRAK-M mediates Toll-like receptor/IL-1R-induced NFκB activation and cytokine production. EMBO J. 32, 583–596 (2013).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  64. Hoarau, C. et al. TLR9 activation induces normal neutrophil responses in a child with IRAK-4 deficiency: involvement of the direct PI3K pathway. J. Immunol. 179, 4754–4765 (2007).

    Article  CAS  PubMed  Google Scholar 

  65. Yamamoto, T. et al. Functional assessment of the mutational effects of human IRAK4 and MyD88 genes. Mol. Immunol. 58, 66–76 (2014).

    Article  CAS  PubMed  Google Scholar 

  66. Moncrieffe, M. C., Grossmann, J. G. & Gay, N. J. Assembly of oligomeric death domain complexes during toll receptor signaling. J. Biol. Chem. 283, 33447–33454 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  67. Xiao, T., Towb, P., Wasserman, S. A. & Sprang, S. R. Three-dimensional structure of a complex between the death domains of Pelle and Tube. Cell 99, 545–555 (1999).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  68. Ngo, V. N. et al. Oncogenically active MYD88 mutations in human lymphoma. Nature 470, 115–119 (2011). This study identifies somatic mutations of MYD88 that cause stimulus-independent signalling and promote cell survival of certain B cell lymphomas.

    Article  CAS  PubMed  Google Scholar 

  69. Treon, S. P. et al. MYD88 L265P somatic mutation in Waldenstrom's macroglobulinemia. New Engl. J. Med. 367, 826–833 (2012).

    Article  CAS  PubMed  Google Scholar 

  70. Tatematsu, M. et al. A molecular mechanism for Toll-IL-1 receptor domain-containing adaptor molecule-1-mediated IRF-3 activation. J. Biol. Chem. 285, 20128–20136 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  71. Meylan, E. et al. RIP1 is an essential mediator of Toll-like receptor 3-induced NF-κ B activation. Nature Immunol. 5, 503–507 (2004).

    Article  CAS  Google Scholar 

  72. Sasai, M. et al. Direct binding of TRAF2 and TRAF6 to TICAM-1/TRIF adaptor participates in activation of the Toll-like receptor 3/4 pathway. Mol. Immunol. 47, 1283–1291 (2010).

    Article  CAS  PubMed  Google Scholar 

  73. Ullah, M. O. et al. The TLR signalling adaptor TRIF/TICAM-1 has an N-terminal helical domain with structural similarity to IFIT proteins. Acta Crystallogr. D Biol. Crystallogr. 69, 2420–2430 (2013).

    Article  CAS  PubMed  Google Scholar 

  74. He, S., Liang, Y., Shao, F. & Wang, X. Toll-like receptors activate programmed necrosis in macrophages through a receptor-interacting kinase-3-mediated pathway. Proc. Natl Acad. Sci. USA 108, 20054–20059 (2011).

    Article  PubMed  Google Scholar 

  75. Gohda, J., Matsumura, T. & Inoue, J. Cutting edge: TNFR-associated factor (TRAF) 6 is essential for MyD88-dependent pathway but not Toll/IL-1 receptor domain-containing adaptor-inducing IFN-β (TRIF)-dependent pathway in TLR signaling. J. Immunol. 173, 2913–2917 (2004).

    Article  CAS  PubMed  Google Scholar 

  76. Sato, S. et al. Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF) associates with TNF receptor-associated factor 6 and TANK-binding kinase 1, and activates two distinct transcription factors, NF-κ B and IFN-regulatory factor-3, in the Toll-like receptor signaling. J. Immunol. 171, 4304–4310 (2003).

    Article  CAS  PubMed  Google Scholar 

  77. Sancho-Shimizu, V. et al. Herpes simplex encephalitis in children with autosomal recessive and dominant TRIF deficiency. J. Clin. Invest. 121, 4889–4902 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  78. Perez de Diego, R. et al. Human TRAF3 adaptor molecule deficiency leads to impaired Toll-like receptor 3 response and susceptibility to herpes simplex encephalitis. Immunity 33, 400–411 (2010).

    Article  CAS  PubMed  Google Scholar 

  79. Zhang, S. Y. et al. TLR3 deficiency in patients with herpes simplex encephalitis. Science 317, 1522–1527 (2007).

    Article  CAS  PubMed  Google Scholar 

  80. Casrouge, A. et al. Herpes simplex virus encephalitis in human UNC-93B deficiency. Science 314, 308–312 (2006).

    Article  CAS  PubMed  Google Scholar 

  81. Schulz, O. et al. Toll-like receptor 3 promotes cross-priming to virus-infected cells. Nature 433, 887–892 (2005).

    Article  CAS  PubMed  Google Scholar 

  82. Jongbloed, S. L. et al. Human CD141+ (BDCA-3)+ dendritic cells (DCs) represent a unique myeloid DC subset that cross-presents necrotic cell antigens. J. Exp. Med. 207, 1247–1260 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  83. Akazawa, T. et al. Antitumor NK activation induced by the Toll-like receptor 3-TICAM-1 (TRIF) pathway in myeloid dendritic cells. Proc. Natl Acad. Sci. USA 104, 252–257 (2007).

    Article  CAS  PubMed  Google Scholar 

  84. Takahashi, K. et al. A protein associated with Toll-like receptor (TLR) 4 (PRAT4A) is required for TLR-dependent immune responses. J. Exp. Med. 204, 2963–2976 (2007).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  85. Wakabayashi, Y. et al. A protein associated with toll-like receptor 4 (PRAT4A) regulates cell surface expression of TLR4. J. Immunol. 177, 1772–1779 (2006).

    Article  CAS  PubMed  Google Scholar 

  86. Randow, F. & Seed, B. Endoplasmic reticulum chaperone gp96 is required for innate immunity but not cell viability. Nature Cell Biol. 3, 891–896 (2001).

    Article  CAS  PubMed  Google Scholar 

  87. Gioannini, T. L. et al. Isolation of an endotoxin-MD-2 complex that produces Toll-like receptor 4-dependent cell activation at picomolar concentrations. Proc. Natl Acad. Sci. USA 101, 4186–4191 (2004).

    Article  CAS  PubMed  Google Scholar 

  88. Correia, J. D. & Ulevitch, R. J. MD-2 and TLR4 N-linked glycosylations are important for a functional lipopolysaccharide receptor. J. Biol. Chem. 277, 1845–1854 (2002).

    Article  CAS  Google Scholar 

  89. Nagai, Y. et al. Essential role of MD-2 in LPS responsiveness and TLR4 distribution. Nature Immunol. 3, 667–672 (2002).

    Article  CAS  Google Scholar 

  90. Liaunardy-Jopeace, A., Bryant, C. E. & Gay, N. J. The COPI/II adaptor protein TMED7 is required to initiate and regulate anterograde trafficking of the immunoreceptor TLR4. Sci. Signal. (in the press).

  91. Wang, D. et al. Ras-related protein Rab10 facilitates TLR4 signaling by promoting replenishment of TLR4 onto the plasma membrane. Proc. Natl Acad. Sci. USA 107, 13806–13811 (2010).

    Article  PubMed  Google Scholar 

  92. Husebye, H. et al. The Rab11a GTPase controls Toll-like receptor 4-induced activation of interferon regulatory factor-3 on phagosomes. Immunity 33, 583–596 (2010).

    Article  CAS  PubMed  Google Scholar 

  93. Husebye, H. et al. Endocytic pathways regulate Toll-like receptor 4 signaling and link innate and adaptive immunity. EMBO J. 25, 683–692 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  94. Zanoni, I. et al. CD14 controls the LPS-induced endocytosis of Toll-like receptor 4. Cell 147, 868–880 (2011). This paper shows that the extrinsic membrane protein CD14 is required for endocytosis of activated TLR4, as well as for the transfer of LPS to MD2.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  95. Tabeta, K. et al. The Unc93b1 mutation 3d disrupts exogenous antigen presentation and signaling via Toll-like receptors 3, 7 and 9. Nature Immunol. 7, 156–164 (2006).

    Article  CAS  Google Scholar 

  96. Lee, B. L. et al. UNC93B1 mediates differential trafficking of endosomal TLRs. eLife 2, e00291 (2013).

    Article  PubMed  PubMed Central  Google Scholar 

  97. Simons, K. & Ikonen, E. Functional rafts in cell membranes. Nature 387, 569–572 (1997).

    Article  CAS  PubMed  Google Scholar 

  98. Munro, S. Lipid rafts: elusive or illusive? Cell 115, 377–388 (2003).

    Article  CAS  PubMed  Google Scholar 

  99. Pike, L. J. & Casey, L. Cholesterol levels modulate EGF receptor-mediated signaling by altering receptor function and trafficking. Biochemistry 41, 10315–10322 (2002).

    Article  CAS  PubMed  Google Scholar 

  100. Hashimoto-Tane, A. et al. T-cell receptor microclusters critical for T-cell activation are formed independently of lipid raft clustering. Mol. Cell. Biol. 30, 3421–3429 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  101. Sun, Y. et al. Free cholesterol accumulation in macrophage membranes activates Toll-like receptors and p38 mitogen-activated protein kinase and induces cathepsin K. Circul. Res. 104, 455–465 (2009).

    Article  CAS  Google Scholar 

  102. Fessler, M. B. & Parks, J. S. Intracellular lipid flux and membrane microdomains as organizing principles in inflammatory cell signaling. J. Immunol. 187, 1529–1535 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  103. Zhu, X. et al. Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol. J. Lipid Res. 51, 3196–3206 (2010).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  104. Bonham, K. S. et al. A promiscuous lipid-binding protein diversifies the subcellular sites of toll-like receptor signal transduction. Cell 156, 705–716 (2014).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  105. Beutler, E., Gelbart, T. & West, C. Synergy between TLR2 and TLR4: a safety mechanism. Blood Cells Mol. Dis. 27, 728–730 (2001).

    Article  CAS  PubMed  Google Scholar 

  106. Betzig, E. et al. Imaging intracellular fluorescent proteins at nanometer resolution. Science 313, 1642–1645 (2006).

    Article  PubMed  Google Scholar 

  107. Rust, M. J., Bates, M. & Zhuang, X. Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM). Nature Methods 3, 793–795 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  108. Hess, S. T., Girirajan, T. P. & Mason, M. D. Ultra-high resolution imaging by fluorescence photoactivation localization microscopy. Biophys. J. 91, 4258–4272 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  109. Geisse, J. et al. Imiquimod 5% cream for the treatment of superficial basal cell carcinoma: results from two phase III, randomized, vehicle-controlled studies. J. Am. Acad. Dermatol. 50, 722–733 (2004).

    Article  PubMed  Google Scholar 

  110. Northfelt, D. W. et al. A Phase 1 dose-finding study of the novel Toll-like receptor 8 agonist VTX 2337 in adult subjects with advanced solid tumors or lymphoma. Clin. Cancer Res. http://dx.doi.org/10.1158/1078-0432.CCR-14-0392 (2014).

  111. Sacre, S. M. et al. Inhibitors of TLR8 reduce TNF production from human rheumatoid synovial membrane cultures. J. Immunol. 181, 8002–8009 (2008).

    Article  CAS  PubMed  Google Scholar 

  112. Casal, E. et al. The crystal structure of the BAR domain from human Bin1/amphiphysin II and its implications for molecular recognition. Biochemistry 45, 12917–12928 (2006).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

This work was supported by programme grants from the Wellcome Trust (WT081744/Z/06/Z) and the UK Medical Research Council (G1000133) to N.J.G. and C.E.B., and a Wellcome Trust Investigator award to N.J.G. (WT100321/Z/12/Z). The authors thank A. Liaunardy-Jopeace for help with Figure 5.

Author information

Authors and Affiliations

  1. Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK

    Nicholas J. Gay, Martyn F. Symmons & Monique Gangloff

  2. Department of Veterinary Medicine, University of Cambridge, Cambridge, CB3 0ES, UK

    Clare E. Bryant

Authors
  1. Nicholas J. Gay
    View author publications

    You can also search for this author inPubMed Google Scholar

  2. Martyn F. Symmons
    View author publications

    You can also search for this author inPubMed Google Scholar

  3. Monique Gangloff
    View author publications

    You can also search for this author inPubMed Google Scholar

  4. Clare E. Bryant
    View author publications

    You can also search for this author inPubMed Google Scholar

Corresponding author

Correspondence to Nicholas J. Gay.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information S1 (Figure)

The effects of two forms of cooperativity acting as a receptor moves from its unbound, pre-activation monomeric state (left) to its activated dimeric state with bound ligand (right) (PDF 288 kb)

PowerPoint slides

Glossary

Protomer

A structural unit of an oligomeric protein. It can be a protein subunit or several different subunits that assemble in a defined stoichiometry to form an oligomer. The protomer is the smallest subset of the different subunits that form the oligomer.

Hoogsteen base pair

An alternative configuration for G–C base pairs in double-stranded nucleic acids. The guanosine base flips around the N-glycosidic bond from the anti to the syn configuration, allowing the formation of a hydrogen bond between the N7 of guanosine and the N3 of cytosine, instead of the N1–N3 hydrogen bond that is found in Watson–Crick base pairs.

Allosteric interactions

Interactions between two topographically distinct binding sites on the same receptor complex. These interactions can be between two ligand binding sites or between a ligand binding site and an effector binding site.

Positive cooperative binding

Cooperative binding occurs if the number of binding sites of a receptor that are occupied by ligand is a nonlinear function of ligand concentration. Positive cooperative binding of a ligand increases the apparent affinity of the receptor (for example, by inducing a conformational change) and hence increases the chance of another ligand molecule binding. The presence of preformed Toll-like receptor 8 dimers in the absence of single-stranded RNA is an example of positive cooperative binding.

Negative cooperative binding

A form of interaction that involves the binding of a ligand that decreases receptor affinity and hence makes the binding of other ligand molecules less likely. The presence of ligand-bound Toll–Spätzle monomers demonstrates negative cooperative binding.

Greek key motif

A common structural motif that consists of four adjacent antiparallel strands and their linking loops. Three antiparallel strands are connected by hairpins, whereas the fourth is adjacent to the first and is linked to the third by a longer loop.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Gay, N., Symmons, M., Gangloff, M. et al. Assembly and localization of Toll-like receptor signalling complexes. Nat Rev Immunol 14, 546–558 (2014). https://doi.org/10.1038/nri3713

Download citation

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nri3713

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing