Amino acids conserved in interleukin-1 receptors (IL-1Rs) and the Drosophila toll protein are essential for IL-1R signal transduction.
The cytoplasmic domain of the human T cell-type interleukin-1 receptor (hIL-1R) is not involved in the binding, internalization, or nuclear localization of interleukin-1 (IL-1), but is essential for signal transduction. We have previously localized a 50-amino acid region (residues 477-527) critical for IL-1-mediated activation of the interleukin-2 promoter in T cells. This region displays a striking degree of amino acid conservation in human, murine, and chicken IL-1Rs. Here we report the results of a site-directed mutational analysis of the cytoplasmic domain of the hIL-1R. We have introduced single-amino acid substitutions at positions conserved in all three receptors and at nonconserved positions and identified key amino acids for IL-1R function in signal transduction. Three basic (Arg431, Lys515, and Arg518) and 3 aromatic (Phe513, Trp514, and Tyr519) amino acids that are conserved in human, murine, and chicken IL-1Rs could not be replaced without abolishing IL-1R-mediated signal transduction. A substitution at another conserved position (Pro521) reduces significantly the ability of the IL-1R to transmit the IL-1 signal. Nonconserved residues could be replaced without affecting signal transduction. The cytoplasmic domain of the IL-1R is related to that of the Drosophila Toll protein, with a 26% identity and a 43% similarity in amino acid sequence. The amino acids shown to be essential for IL-1R function are conserved in the Toll protein. Our experimental data indicate that the amino acid sequence similarity between the IL-1R and the Drosophila toll protein reflects a functional homology between the two proteins.
Heguy
A
A
Sclavo Research Center, Siena, Italy.
Baldari
C T
CT
Macchia
G
G
Telford
J L
JL
Melli
M
M
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002855:Chromatography, Thin Layer; D004330:Drosophila; D029721:Drosophila Proteins; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D007301:Insect Hormones / Q000235:genetics / Q000378:metabolism*; D007375:Interleukin-1 / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D017472:Receptors, Interleukin-1; D011994:Recombinant Proteins / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D051193:Toll-Like Receptors; D014407:Tumor Cells, Cultured
D000596:Amino Acids; D029721:Drosophila Proteins; D007301:Insect Hormones; D007375:Interleukin-1; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D017472:Receptors, Interleukin-1; D011994:Recombinant Proteins; C068721:Tl protein, Drosophila; D051193:Toll-Like Receptors