BST2 and cancer: Based on the structural information of B49Mod1, which contains three cysteine residues (9CYS, 19CYS, 47CYS, corresponding to 53CYS, 63CYS, and 91CYS in BST-2) and the importance of the BST-2 ECD cysteine residues, especially 91CYS, on cancer cell adhesion [29], we used trypsin-mediated degradation studies to truncate B49Mod1 into six smaller fragments as the first step of the structure-activity relationship (SAR) studies.