(a) Depiction of the alignment of IFN-λ1, 2 and 3 to one another. Exclamation points below the sequence indicates the location of sites where mutation of IFN-λ3 has been shown to impact activity. Identical amino acid residues are shown in green, glycosylation sites in pink, signal peptide in purple, variations in red, and cysteines in yellow, purple indicates residues not visualized to date in any known structure. Blue lettering above the sequences indicates the location and type of secondary structure element found in IFN-λ or IFN-λR1, with b indicating a beta strand and h indicating the presence of a helix. * indicates a conserved residue, : indicates a partially conserved residue, and . indicates the presence of similar residues. Disulfide bridges in IFN-λ1_Human: Cys15 is free, Cys-49-Cys145, Cyst112–171. Disulfide bridges in IFN-λ3_Human: Cys16-Cys115, Cys50 is free, Cys50–148, Cys167–174 29. Swissprot 66 accession numbers are Q8IU54 for IFN-λ1_Human, Q8IZJ0 for IFN- λ2_Human and Q8IZI9 for IFN-λ3_Human. (b) Alignment of the ectodomain of IFN-λR1 to the equivalent domains in IL-10R1, IL-10R2, and IL-22R1. Magenta lettering in this alignment indicates regions that have not been visualized in the available crystal structures. Cysteines are highlighted in yellow. Symbols below the alignment are identical to those in (a).

Surface comparison is based on the data of Yoon et al. 28. Clefts identified as being important for receptor promiscuity in IL-10R2 (labeled in IL-10R2) are not found in IFN-λR1 or Il-10R1. The identities of the models are shown below.

(a) IFN-λ1 is in green, IFN-λR1 in cyan, glycosylation sites in blue (Asn) and yellow (carbohydrates), glycerol in magenta, disulfide bonds as yellow spheres, IFN-λ1 residues at the interface in orange, and IFN-λR1 residues at the interface in red. Amino acid side chains, carbohydrates, and solvent molecules are depicted in stick format. The location of the site I and site II interfaces are labeled. (b) The structure of IFN-λ1, in the same orientation as is found in (a). The helices found in the ligand are labeled A through F with the N and C-termini also labeled. (c) The structure of IFN-λR1, in the same orientation as found in (a). The loops found in the receptor are labeled, from L1 to L13. The N and C-termini are labeled as well. Disulfide bonds are depicted as yellow sticks.

IFN-λ1 is depicted in green while IFN-λR1 is depicted in cyan, with residues making contacts depicted in stick format. Oxygens are colored in red and nitrogens are colored blue. (a) Site 1 interactions are depicted, with hydrogen bonds formed between the ligand and receptor depicted as dashed lines and their distances listed. (b) Site 2 interactions between ligand and receptor are shown, with identical coloring as in (a).

An alignment of IFN-λR1 to IL-10R1 was performed and the positions of their respective ligands, IFN-λ1 and IL-10 were added. IL-10 is a composite containing helices A through D of one monomer of IL-10, and helices E and F of the dimeric partner. The IFN-λ1/IFN-λR1 complex is displayed in green/cyan and the IL-10/IL-10R1 complex is displayed in yellow/rose. For IL-10/IL10-R1, only one half of the IL-10 dimer is displayed.