Identification of Two Major Sites in the Type I Interleukin-1 Receptor Cytoplasmic Region Responsible for Coupling to Pro-inflammatory Signaling Pathways

Abstract

Type I interleukin-1 receptor is the prototype for a family of proteins, which play a central role in early responses to injury and infection. The similarity of function across the family is reflected in similarity in signaling: all members tested couple to activation of NFB and stress kinases. The coupling to these pathways is mediated by a 200-residue intracellular domain (the Toll/ interleukin-1 receptor domain), in which sequence conservation is primarily confined to three short motifs (boxes 1, 2, and 3) located at amino acid residue positions 10 (box 1), 60 (box 2), and 170 (box 3). We have analyzed the contribution of these motifs to function by alanine scanning mutagenesis of the human interleukin-1 receptor type I. Mutant receptors were tested for expression, ligand binding, activation of receptor-associated kinase(s), NFB, stress kinases, and transcription. Mutations in all three motifs led to low cell surface expression. Mutants in box 3 were, however, wild type for signaling, whereas mutants in boxes 1 and 2 were defective. We conclude that the conserved motifs box 1 and box 2 mediate the coupling of molecules in the family to inflammation signaling pathways.

Cloning and characterization of the grass carp (Ctenopharyngodon idella) Toll-like receptor 22 gene, a fish-specific gene

“…The TIR domain, which is functionally important for TLR signal transduction, contains three active motifs: box 1 (FDAFISY), box 2 (LC-RD-PG), and box 3 (a conserved W surrounded by basic residues) [34]. It has been suggested that box 1 and box 2 mediate binding to receptor molecules of signaling transduction pathways, while box 3 has been shown to be primarily involved in directing localization of receptors [34]. These active motifs were basically conserved in CiTLR22 (box 1, Y 802 DAFISY 808 ; box 2, L 832 C-RD-PG 842 and box 3, W 934 surrounded by basic residue K940), and TLR22 of other fish species.…”

Toll-Like Receptors in Health and Disease: Complex Questions Remain

“…Despite the prevalent notion that TIR domains are highly conserved, the homology of these regions between TIR-containing receptors is actually relatively low, and although there are more focused areas of conservation in key regions involved in signaling, these TIR domains provide ample room for TLR-type specific interactions with downstream signal components (49). To date, much of our knowledge of these signaling pathways is derived from studies of knockout mice (natural or engineered).…”

Toll-like receptor signal transduction

“…Most TIR Box 2 sequences have a conserved proline, which when mutated to histidine renders the protein unable to signal. The function of Box 3 is not fully understood, although it contains residues important in signaling (based on mutational analysis of the type I IL-1 receptor) (Slack et al, 2000) (Figure 1). …”