Schematic of the BST-2 structure. (A) BST-2 is a type 2 integral membrane protein. The N-terminus localizes to the cytoplasm. The BST-2 ectodomain contains three cysteine residues (C53, C63, C91) and two potential sites for N-linked glycosylation (N65, N92). The C-terminus of BST-2 is modified by the addition of a glycosyl-phosphatidylinositol (gpi) anchor. (B) Predicted amino acid sequence of human BST-2. The predicted transmembrane region is indicated by a box. Signals for N-linked glycosylation are marked in blue; cysteine residues in the BST-2 extracellular domain are highlighted in yellow. The arrow points to the predicted site of cleavage for the addition of the gpi anchor .