The human X chromosome linked Inhibitor of Apoptosis Protein (XIAP) is a major member of the inhibitor of apoptosis (IAP) family. XIAP functions by direct binding and inhibition of several caspases, including Caspase 3, Caspase 7 and Caspase 9. During apoptosis XIAP is specifically cleaved by Caspase 3 and partially loses its function. In addition to blocking the apoptosis signaling pathway, XIAP can also bind several other proteins in the bone morphogenetic protein (BMP) signaling pathway and act as a coupler between the membrane BMP receptor and the TAB1 TAK1 complex by binding to these proteins.