FunctionPotent inhibitor of cell death. Inhibits activation of caspases (By similarity). Appears to regulate cell death by blocking the voltage-dependent anion channnel (VDAC) by binding to it and preventing the release of the caspase activator, CYC1, from the mitochondrial membrane. Isoform Bcl-X(S) promotes apoptosis.
Tissue specificityBcl-X(S) is expressed at high levels in cells that undergo a high rate of turnover, such as developing lymphocytes. In contrast, Bcl-X(L) is found in tissues containing long-lived postmitotic cells, such as adult brain.
Sequence similaritiesBelongs to the Bcl-2 family.
DomainThe BH4 motif is required for anti-apoptotic activity. The BH1 and BH2 motifs are required for both heterodimerization with other Bcl-2 family members and for repression of cell death.
Post-translational modificationsProteolytically cleaved by caspases during apoptosis. The cleaved protein, lacking the BH4 motif, has pro-apoptotic activity.
Cellular localizationMitochondrion membrane. Nucleus membrane. Mitochondrial membranes and perinuclear envelope.