The STIR-domain superfamily in signal transduction, development and immunity

We have identified a conserved sequence segment in transmembrane receptors (including SEFs, IL17Rs) and soluble factors (including CIKS/ACT1) in eukaryotes and bacteria – the SEFIR domain. This sequence domain is part of the new STIR domain superfamily comprising also the TIR domain known to mediate TIR–TIR homotypic interactions. In TOLL/IL1R-like pathways, the cytoplasmically localized TIR domain of a receptor and the TIR domain of a soluble adaptor interact physically and activate signalling. The similarity between the SEFIR and TIR domains involves the conserved boxes 1 and 2 of the TIR domain that are implicated in homotypic dimerization, but there is no sequence similarity between SEFIR domains and the TIR sequence box 3. By analogy, we suggest that SEFIR-domain proteins function as signalling components of Toll/IL-1R-similar pathways and that their SEFIR domain mediates physical protein–protein interactions between pathway components.