Structural comparison of TRAIL between X laevis and other vertebrates. (A) Comparison of the protein structures of X laevis (x) and human (h) TRAIL. The black and shaded boxes show the transmembrane domain and TNF domain, respectively. The numbers above and within the box indicate the amino-acid residues and percentage identity between human TRAIL and xTRAILs, respectively. (B) A phylogenetic tree of TNF family members constructed by the neighbor-joining method. Xl indicates X laevis; Hs, Homo sapiens; Mm, Mus musculus; Gg, Gallus gallus; and Dr, Danio rerio.