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).