Apoptosis regulator Bcl-X - Bcl-2 homologous antagonist/killer heterodimer

The anti-apoptotic Bcl-xl - Bak heterodimer is present on the mitochondrial membrane. Bcl-xl is responsible for binding the pro-apoptotic Bak protein in healthy cells. During apoptosis BH3-only proteins (BIM, BAD, etc..) will bind to Bcl-xl and cause Bak to be released. Upon release, Bak will oligomerize creating pores in the mitochondrial membrane which facilitate the release of Cytochrome c.

Swiss-Prot Accession Number: Q07817(Bcl-xl); Q16611(Bak)