title: BIM and tBID are not mechanistically equivalent when assisting BAX to permeabilize bilayer membranes.
abstract: BIM and tBID are two BCL-2 homology 3 (BH3)-only proteins with a particularly strong capacity to trigger BAX-driven mitochondrial outer membrane permeabilization, a crucial event in mammalian apoptosis. However, the means whereby BIM and tBID fulfill this task is controversial. Here, we used a reconstituted liposomal system bearing physiological relevance to explore systematically how the BAX-permeabilizing function is influenced by interactions of BIM/BID-derived proteins and BH3 motifs with multidomain BCL-2 family members and with membrane lipids. We found that nanomolar dosing of BIM proteins sufficed to reverse completely the inhibition of BAX permeabilizing activity exerted by all antiapoptotic proteins tested (BCL-2, BCL-X(L), BCL-W, MCL-1, and A1). This effect was reproducible by a peptide representing the BH3 motif of BIM, whereas an equivalent BID BH3 peptide was less potent and more selective, reversing antiapoptotic inhibition. On the other hand, in the absence of BCL-2-type proteins, BIM proteins and the BIM BH3 peptide were inefficient, directly triggering the BAX-permeabilizing function. In contrast, tBID alone potently assisted BAX to permeabilize membranes at least in part by producing a structural distortion in the lipid bilayer via BH3-independent interaction of tBID with cardiolipin. Together, these results support the notion that BIM and tBID follow different strategies to trigger BAX-driven mitochondrial outer membrane permeabilization with strong potency.
authors.affiliation: Unidad de Biofísica (Centro Mixto Consejo Superior de Investigaciones Cientificas, Universidad del Pais Vasco/Euskal Herriko Unibertsitatea), Universidad del Pais Vasco/Euskal Herriko Unibertsitatea, 48080 Bilbao, Spain.
authors.forename: Oihana
authors.initials: O
authors.lastname: Terrones
authors.forename: Aitor
authors.initials: A
authors.lastname: Etxebarria
authors.forename: Ane
authors.initials: A
authors.lastname: Landajuela
authors.forename: Olatz
authors.initials: O
authors.lastname: Landeta
authors.forename: Bruno
authors.initials: B
authors.lastname: Antonsson
authors.forename: Gorka
authors.initials: G
authors.lastname: Basañez
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D002308:Cardiolipins / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000502:physiology*; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C000606775:BCL2L11 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494828:Bax protein, rat; D000072224:Bcl-2-Like Protein 11; C000606778:Bcl2l11 protein, rat; D002308:Cardiolipins; D008081:Liposomes; D008565:Membrane Proteins; D010455:Peptides; D011518:Proto-Oncogene Proteins; D051028:bcl-2-Associated X Protein