Apoptosis sounds like a brutal death for a cell—all of that blebbing, fragmentation, and destruction just gives me the willies. Most of the time, cells only go through apoptosis when absolutely necessary thanks to proteins such as Bcl-xL. A recent paper finds a new, non-apoptosis role for Bcl-xL in cell health and survival.
The Bcl-2 family is made up of proteins that can either drive or inhibit apoptosis, which is programmed cell death. Bcl-xL is a Bcl-2 family member that inhibits apoptosis by binding Bax, a pro-apoptosis family member, at the outer membrane of mitochondria. There, Bcl-xL inhibits the release of cytochrome c, which during apoptosis serves to kick-start a cascade that destroys the cell. A recent paper finds an exciting new role for Bcl-xL outside of apoptosis. Chen and colleagues found Bcl-xL localized to the inner mitochondrial membrane, contrary to previous opinion that it is only found at the outer mitochondrial membrane. At the inner membrane, Bcl-xL is important in maintaining the efficiency of the mitochondria by inhibiting excessive flux of ions across the inner membrane. The images above are electron micrographs of mitochondria. Antibodies that label Bcl-xL are bound to tiny gold beads, which are found at the inner membrane (black arrows), as well as the outer membrane (arrowheads) and adjacent membranes (line arrows).
Chen, Y., Aon, M., Hsu, Y., Soane, L., Teng, X., McCaffery, J., Cheng, W., Qi, B., Li, H., Alavian, K., Dayhoff-Brannigan, M., Zou, S., Pineda, F., O'Rourke, B., Ko, Y., Pedersen, P., Kaczmarek, L., Jonas, E., & Hardwick, J. (2011). Bcl-xL regulates mitochondrial energetics by stabilizing the inner membrane potential originally published in The Journal of Cell Biology, 195 (2), 263-276 DOI: 10.1083/jcb.201108059
amazing!
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