WAP domain of the trappin gene family. WAP domains of SLPI (A), trappin-related genes (B), trappin-2 (C), and the other species-specific trappin paralogs (D) are shown. Conserved and semiconserved residues among trappin-2 genes are indicated by light gray. Eight conserved Cys residues constituting the WAP motif signature sequence are shaded in black. The asterisk indicates the catalytically important Met residue. The variable region, which is thought to determine the specificity of WAP motifs, is boxed.