Domain:The 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. ,Function:Potent inhibitor of cell death. Isoform Bcl-X (L) anti-apoptotic activity is inhibited by association with SIVA isoform 1. 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 , cytochrome c , from the mitochondrial membrane. The Bcl-X (S) isoform promotes apoptosis. ,PTM:Proteolytically cleaved by caspases during apoptosis. The cleaved protein , lacking the BH4 motif , has pro-apoptotic activity. ,similarity:Belongs to the Bcl-2 family. ,subcellular location:Mitochondrial membranes and perinuclear envelope. ,subunit:Bcl-X (L) forms homodimers , and heterodimers with BAX , BAK and BCL2. Heterodimerization with BAX does not seem to be required for anti-apoptotic activity. Also interacts with BAD and BBC3. Isoform Bcl-X (L) binds to Siva isoform 1. Interacts with BCL2L11 (By similarity) . Interacts with BECN1 and PGAM5. Isoform Bcl-X (L) interacts with BAX isoform Sigma. ,tissue specificity:Bcl-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. ,
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