Apoptosis (cell suicide) is such an important decision to the cell, it uses a rheostat to control the decision instead of a simple ON-OFF switch. The mechanism involves multidomain BCL2 family proteins like Mcl-1 rendered here, and pro-death proteins like Bim. In this rendering, only the 24-residue BH3 alpha-helix of Bim (lavendar) is shown; it forms an amphipathic helix. Bim fits snugly into the hydrophobic pocket of Mcl-1, comprised of the hydrophobic sidechains of Mcl-1 helices a2, a4, and a5. These sidechains jut into the groove, forming a cozy landing platform for Bim. This is a protein-protein interaction (PPI) "hotspot"--an interface for drug discovery.