FIGURE 2.

Structure analysis of LcIFNd. (A) Structure of LcIFNd in cartoon representation. Secondary structural elements are labeled A–F. The N terminus and C terminus are indicated with N and C, respectively. One disulfide bond is colored yellow and shown in detail with surrounding residues as 2Fo-Fc electron density maps contoured at the 1.0 σ level. (B) Superimposition of LcIFNd (firebrick) with LcIFNi (PDB ID: 7WZ5, marine), zIFN-φ1 (PDB ID: 3PIV, dark violet), zIFN-φ2 (PDB ID: 3PIW, gray 90), CiIFNa (PDB ID: 7WKH, aquamarine), hIFN-α2 (PDB ID: 1RH2, split-pea), hIFN-ω (PDB ID: 3SE4, tv-orange), hIFN-β (PDB ID: 1AU1, cyan-light teal), and mIFN-β (PDB ID: 1IFA, light orange). All structures were superimposed in PyMOL using the “align” command. (C) Left, Superimposition of LcIFNd, zIFN-φ1, CiIFNa, and mIFN-β. Right, Superimposition of LcIFNi, zIFN-φ2, hIFN-α2, hIFN-ω, and hIFN-β. (D) Multiple alignment of mature peptide sequence of LcIFNd with other fish type I IFNs whose crystal structures have been resolved. The conserved cysteine residues involved in forming intramolecular disulfide bonds are indicated by paired lines (C1–C3, C2–C4, and C5–C6) and highlighted in yellow. The cysteine residues C1 and C3 are marked with a star (★)below the alignment. (E) Representation of the C1–C3 disulfide bond in LcIFNd (yellow) superimposed with LcIFNi (a, orange), zIFN-φ1 (b, orange), zIFN-φ2 (c, orange), and CiIFNa (d, orange).