Bcl-xL is a 30 kDa anti-apoptotic protein belonging to the Bcl-2 family. Bcl-xL prevents apoptosis throμgh two different mechanisms: by heterodimerization with an apoptotic protein to inhibit its apoptotic effect, and by its direct pore-forming effect on the outer-membrane of mitochondria to help maintain a normal membrane state under stress conditions. Bcl-xL can be cleaved by caspases upon apoptotic activation, which converts Bcl-xL from an antiapoptotic protein to a proapoptotic cleavage product. The cleavage product of Bcl-xL forms cytochrome c-releasing pores in the mitochondrial membrane to facilitate the apoptosis signaling pathway.