Site-Dependent Cysteine Lipidation Potentiates the Activation of Proapoptotic BAX

BCL-2 family proteins converge at the mitochondrial outer membrane to regulate apoptosis and maintain the critical balance between cellular life and death. This physiologic process is essential to organism homeostasis and relies on protein-protein and protein-lipid interactions among BCL-2 family proteins in the mitochondrial lipid environment. Here, we find that trans-2-hexadecenal (t-2-hex), previously implicated in regulating BAX-mediated apoptosis, does so by direct covalent reaction with C126, which is located on the surface of BAX at the junction of its alpha 5/alpha 6 core hydrophobic hairpin. The application of nuclear magnetic resonance spectroscopy, hydrogen-deuterium exchange mass spectrometry, specialized t-2-hex-containing liposomes, and BAX mutational studies in mitochondria and cells reveals structure-function insights into the mechanism by which covalent lipidation at the mitochondria sensitizes direct BAX activation. The functional role of BAX lipidation as a control point of mitochondrial apoptosis could provide a therapeutic strategy for BAX modulation by chemical modification of C126.