Bak breaks up mitochondrion, while Bax opens holes to induce cell death.

Researchers found that when a cell is seriously stressed, a protein called Bak, may set it up for apoptosis. Bak initially chops the mitochondrion into vulnerable little spheres. Another protein, Bax, then pokes countless holes in those spheres, spilling their pro-apoptosis contents into the cell.

To stress cells in the study, a team from the Medical College of Georgia blocked oxygen supplies and used cisplatin. They then documented that filamentous mitochondria became fragmented early and quickly in apoptosis. They also found the deadly fragmentation results in Bak’s interaction with mitochondria-shaping proteins called mitofusins, which help mitochondria keep their filamentous shape in nonstressed cells. The scientists believe that Bak may also play a role in mitofusin regulation in normal, nonstressful conditions.

Looking at kidney cells and neurons in a Bak deficient mouse, the investigators went on to show that Bak and Bax need each other to successfully spawn cell suicide. “If you have Bak but not Bax, the mitochondria still fragment but they don’t die. If you have Bax but not Bak, you still have punctures in the mitochondria but with low efficiency,” says Craig Brooks,  graduate student and the paper’s first author.

The paper was published in Proceedings of the National Academy of Sciences.

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