Tailor-made designer helical peptides that induce mitochondrion-mediated cell death without necrosis

Managing protein-protein interactions is essential for resolving unknown biological events at the molecular level and developing drugs. We have designed and synthesized a side-chain-crosslinked helical peptides based on the binding domain of a pro-apoptotic protein (Bad) that induces programmed cell death. The peptide showed high helical content and bound to its target, Bcl-XL, more strongly than its non-crosslinked counterparts. When HeLa cells were incubated with the crosslinked peptide, the peptide entered the cytosol across the plasma membrane. The peptide formed a stable complex with Bcl-XL localized at the outer mitochondrial membrane, and this binding event caused the release of cytochrome c from the intermembrane space of mitochondria into the cytosol. This activated the caspase cascade: 70% of HeLa cells died by the apoptosis pathway (without evidence of necrosis).