Mal and MyD88: adapter proteins involved in signal transduction by Toll-like receptors.
Signal transduction processes activated by Toll-like receptors (TLRs) include the important transcription factor NF-kappaB and 2 MAP kinases, p38 and Jun N-terminal kinase. These signals ultimately give rise to increased expression of a multitude of pro-inflammatory proteins. Receptor-proximal proteins involved in signalling by all TLRs include the adapter MyD88, 3 IRAKs (IRAK-4, IRAK and IRAK-2), Tollip, Traf-6 and TAK-1. Differences between signals generated by TLRs are emerging, with both TLR4 and TLR2 signalling requiring an additional adapter termed MyD88-adapter-like (Mal; also known as TIRAP). MyD88 and Mal both have a homologous Toll/IL-1 receptor (TIR) domain although they differ in their N-termini, with MyD88 possessing a death domain. In addition, structural models reveal marked differences in surface charges which, when taken with surface charge differences between TLR2 and TLR4 TIR domains, may indicate that TLR4 but not TLR2 recruits Mal directly. Another difference is that Mal can become phosphorylated. Future studies on Mal will reveal specificities in signal transduction by different TLRs, which may ultimately provide molecular explanations for specificities in the innate immune response to infection.
O'Neill
Luke A J
LA
Department of Biochemistry, Trinity College Dublin, Ireland. laoneill@tcd.ie
Dunne
Aisling
A
Edjeback
Michael
M
Gray
Pearl
P
Jefferies
Caroline
C
Wietek
Claudia
C
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000943:Antigens, Differentiation / Q000502:physiology*; D006801:Humans; D008070:Lipopolysaccharides / Q000276:immunology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D053594:Myeloid Differentiation Factor 88; D011956:Receptors, Cell Surface / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*; D017472:Receptors, Interleukin-1 / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
D048868:Adaptor Proteins, Signal Transducing; D000943:Antigens, Differentiation; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D008562:Membrane Glycoproteins; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D017472:Receptors, Interleukin-1; C434984:TIRAP protein, human; C499045:TIRAP protein, mouse; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors