TNF receptor-associated factor 1 (TRAF1) plays a role in the regulation of cell survival and apoptosis []. TRAF1 is unique among TRAF proteins in that it lacks a RING domain found in the N-terminal regions of other TRAFs []. The heterotrimer formed by TRAF1 and TRAF2 is part of a E3 ubiquitin-protein ligase complex that promotes ubiquitination of target proteins, such as MAP3K14 [, ].TRAF1 is unique among the TRAFs in that it lacks a RING domain, which is critical for the activation of nuclear factor-kappaB and Jun NH2-terminal kinase. Studies on TRAF1-deficient mice suggest that TRAF1 has a negative regulatory role in TNFR-mediated signaling events []. TRAF1 contains one zinc finger and one TRAF domain.
TNF receptor-associated factor 1 (TRAF1) plays a role in the regulation of cell survival and apoptosis []. TRAF1 is unique among TRAF proteins in that it lacks a RING domain found in the N-terminal regions of other TRAFs []. The heterotrimer formed by TRAF1 and TRAF2 is part of a E3 ubiquitin-protein ligase complex that promotes ubiquitination of target proteins, such as MAP3K14 [, ].TRAF1 is unique among the TRAFs in that it lacks a RING domain, which is critical for the activation of nuclear factor-kappaB and Jun NH2-terminal kinase. Studies on TRAF1-deficient mice suggest that TRAF1 has a negative regulatory role in TNFR-mediated signaling events []. TRAF1 contains one zinc finger and one TRAF domain.The TRAF domain can be divided into a more divergent N-terminal alpha helical region (TRAF-N), and a highly conserved C-terminal MATH subdomain (TRAF-C) with an eight-stranded β-sandwich structure. TRAF-N mediates trimerization while TRAF-C interacts with receptors [, ].
The tumour necrosis factor (TNF) receptor associated factors (TRAFs) are major signal transducers for the TNF receptor (TNFR) superfamily and the interleukin-1 receptor/Toll-like receptor superfamily in mammals []. TRAFs constitute a family of genetically conserved adapter proteins found in mammals (TRAF1-6) as well as in other multicellular organisms such as Drosophila [], Caenorhabditis elegans []. TRAF2 is the prototypical member of the family. Mammalian TRAF1 and TRAF2 were the first members initially identified by their association with TNFR2. The TRAF1/TRAF2 and TRAF3/TRAF5 gene pairs may have arisen from recent independent gene duplications and to share a common ancestral gene. TRAF4 and TRAF6 precursor genes may have arisen earlier during evolution, with the divergence of the TRAF6 precursor occurring earliest of all. Except TRAF1, this PIRSF has a general domain architecture containing one N-terminal RING finger, a variable number of middle region of TRAF-type zinc finger and C2H2 type of zinc finger, and one C-terminal MATH domain. TRAF1 is unique in the family in that it lacks the N-terminal RING and zinc-finger domains []. This has rendered TRAF1 unable to promote TNF receptor signalling and act as a "dominant negative"TRAF []. Also TRAF1 is a substrate for caspases activated by TNF family death receptors []. The larger C-terminal cleaved fragment can bind to and sequester TRAF2 from TNFR1 complex, therefore modulating TNF induced NFkB activation []. A wide range of biological functions, such as adaptive and innate immunity, embryonic development, stress response and bone metabolism, are mediated by TRAFs through the induction of cell survival, proliferation, differentiation and death. TRAFs are functionally divergent from a perspective of both upstream and downstream TRAF signal transduction pathways and of signalling-dependent regulation of TRAF trafficking. Each TRAF protein interacts with and mediates the signal transduction of multiple receptors, and in turn each receptor utilises multiple TRAFs for specific functions []. About 40 interaction partners of TRAF have been described thus far, including receptors, kinases, regulators and adaptor proteins.TRAF proteins can be recruited to and activated by ligand-engaged receptors in least three distinct ways []. 1) Members of the TNFR superfamily that do not contain intracellular death domains, such as TNFR2 and CD40, recruit TRAFs directly via short sequences in their intracellular tails []. 2) Those that contain an intracellular death domain, such as TNFR1, first recruit an adapter protein, TRADD, via a death-domain-death-domain interaction, which then serves as a central platform of the TNFR1 signalling complex, which assembles TRAF2 and RIP for survival signalling, and FADD and caspase-8 for the induction of apoptosis. 3) Members of the IL-1R/TLR superfamily contain a protein interaction module known as the TIR domain, which recruits, sequentially, MyD88, a TIR domain and death domain containing protein, and IRAKs, adapter Ser/Thr kinases with death domains. IRAKs in turn associate with TRAF6 to elicit signalling by IL-1 and pathogenic components such as LPS. A common mechanism for the membrane-proximal event in TRAF signalling has been revealed by the conserved trimeric association in the crystal structure of the TRAF domain of TRAF2 [].This entry represents the TNF receptor associated factors found in metazoa.
The tumour necrosis factor (TNF) receptor associated factors (TRAFs) are major signal transducers for the TNF receptor (TNFR) superfamily and the interleukin-1 receptor/Toll-like receptor superfamily in mammals []. TRAFs constitute a family of genetically conserved adapter proteinsfound in mammals (TRAF1-6) as well as in other multicellular organisms such as Drosophila [], Caenorhabditis elegans []. TRAF2 is the prototypical member of the family. Mammalian TRAF1 and TRAF2 were the first members initially identified by their association with TNFR2. The TRAF1/TRAF2 and TRAF3/TRAF5 gene pairs may have arisen from recent independent gene duplications and to share a common ancestral gene. TRAF4 and TRAF6 precursor genes may have arisen earlier during evolution, with the divergence of the TRAF6 precursor occurring earliest of all. Except TRAF1, this PIRSF has a general domain architecture containing one N-terminal RING finger, a variable number of middle region of TRAF-type zinc finger and C2H2 type of zinc finger, and one C-terminal MATH domain. TRAF1 is unique in the family in that it lacks the N-terminal RING and zinc-finger domains []. This has rendered TRAF1 unable to promote TNF receptor signalling and act as a "dominant negative"TRAF []. Also TRAF1 is a substrate for caspases activated by TNF family death receptors []. The larger C-terminal cleaved fragment can bind to and sequester TRAF2 from TNFR1 complex, therefore modulating TNF induced NFkB activation []. A wide range of biological functions, such as adaptive and innate immunity, embryonic development, stress response and bone metabolism, are mediated by TRAFs through the induction of cell survival, proliferation, differentiation and death. TRAFs are functionally divergent from a perspective of both upstream and downstream TRAF signal transduction pathways and of signalling-dependent regulation of TRAF trafficking. Each TRAF protein interacts with and mediates the signal transduction of multiple receptors, and in turn each receptor utilises multiple TRAFs for specific functions []. About 40 interaction partners of TRAF have been described thus far, including receptors, kinases, regulators and adaptor proteins.TRAF proteins can be recruited to and activated by ligand-engaged receptors in least three distinct ways []. 1) Members of the TNFR superfamily that do not contain intracellular death domains, such as TNFR2 and CD40, recruit TRAFs directly via short sequences in their intracellular tails []. 2) Those that contain an intracellular death domain, such as TNFR1, first recruit an adapter protein, TRADD, via a death-domain-death-domain interaction, which then serves as a central platform of the TNFR1 signalling complex, which assembles TRAF2 and RIP for survival signalling, and FADD and caspase-8 for the induction of apoptosis. 3) Members of the IL-1R/TLR superfamily contain a protein interaction module known as the TIR domain, which recruits, sequentially, MyD88, a TIR domain and death domain containing protein, and IRAKs, adapter Ser/Thr kinases with death domains. IRAKs in turn associate with TRAF6 to elicit signalling by IL-1 and pathogenic components such as LPS. A common mechanism for the membrane-proximal event in TRAF signalling has been revealed by the conserved trimeric association in the crystal structure of the TRAF domain of TRAF2 [].
Zinc finger (Znf) domains are relatively small protein motifs which contain multiple finger-like protrusions that make tandem contacts with their target molecule. Some of these domains bind zinc, but many do not; instead binding other metals such as iron, or no metal at all. For example, some family members form salt bridges to stabilise the finger-like folds. They were first identified as a DNA-binding motif in transcription factor TFIIIA from Xenopus laevis (African clawed frog), however they are now recognised to bind DNA, RNA, protein and/or lipid substrates [, , , , ]. Their binding properties depend on the amino acid sequence of the finger domains and of the linker between fingers, as well as on the higher-order structures and the number of fingers. Znf domains are often found inclusters, where fingers can have different binding specificities. There are many superfamilies of Znf motifs, varying in both sequence and structure. They display considerable versatility in binding modes, even between members of the same class (e.g. some bind DNA, others protein), suggesting that Znf motifs are stable scaffolds that have evolved specialised functions. For example, Znf-containing proteins function in gene transcription, translation, mRNA trafficking, cytoskeleton organisation, epithelial development, cell adhesion, protein folding, chromatin remodelling and zinc sensing, to name but a few []. Zinc-binding motifs are stable structures, and they rarely undergo conformational changes upon binding their target. This entry represents TRAF-type zinc finger domains. Some of the proteins that have this domain are mammalian signal transducers associated with the cytoplasmic domain of the 75kDa tumour necrosis factor receptor []. A heterocomplex, homodimer or heterodimer of TRAF1 and TRAF2, binds to the N-terminal of the inhibitor of apoptosis proteins 1 and 2 (IAPS) and recruits them to the tumour necrosis factor receptor 2. Other proteins containing this domain include F45G2.6 protein from Caenorhabditis elegans and DG17 protein from Dictyostelium discoideum (Slime mold).
