PFIC II mutations reside in regions highly conserved throughout the vertebrate phylum. (a) Sequence alignment of mutation sites in BSEP/Bsep from human, rat, mouse, rabbit, and skate using the Clustal alignment software MegAlign (DNASTAR Inc., Madison, Wisconsin, USA). The PFIC II mutations in human BSEP and the corresponding residues in other Bseps are shown in bold. (b) The positions of G238V, E297G, C336S, D482G, G982R, R1153C, and R1268Q are indicated by stars in a predicted topology model of rat Bsep. The Walker A and Walker B regions are shown in boxes, and a number of potential glycosylation sites are indicated by the branch structures in the first extracellular loop of Bsep. The predicted 12 transmembrane-spanning segments in Bsep are shown in boxes labeled 1–12.