title: Ligand binding and membrane insertion compete with oligomerization of the BclXL apoptotic repressor.
abstract: B-cell lymphoma extra large (BclXL) apoptotic repressor plays a central role in determining the fate of cells to live or die during physiological processes such as embryonic development and tissue homeostasis. Herein, using a myriad of biophysical techniques, we provide evidence that ligand binding and membrane insertion compete with oligomerization of BclXL in solution. Of particular importance is the observation that such oligomerization is driven by the intermolecular binding of its C-terminal transmembrane (TM) domain to the canonical hydrophobic groove in a domain-swapped trans fashion, whereby the TM domain of one monomer occupies the canonical hydrophobic groove within the other monomer and vice versa. Binding of BH3 ligands to the canonical hydrophobic groove displaces the TM domain in a competitive manner, allowing BclXL to dissociate into monomers upon hetero-association. Remarkably, spontaneous insertion of BclXL into DMPC/DHPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine/1,2-dihexanoyl-sn-glycero-3-phosphocholine) bicelles results in a dramatic conformational change such that it can no longer recognize the BH3 ligands in what has come to be known as the "hit-and-run" mechanism. Collectively, our data suggest that oligomerization of a key apoptotic repressor serves as an allosteric switch that fine-tunes its ligand binding and membrane insertion pertinent to the regulation of apoptotic machinery.
authors.affiliation: Department of Biochemistry and Molecular Biology and USylvester Braman Family Breast Cancer Institute, Leonard Miller School of Medicine, University of Miami, Miami, FL 33136, USA.
authors.forename: Vikas
authors.initials: V
authors.lastname: Bhat
authors.forename: Caleb B
authors.initials: CB
authors.lastname: McDonald
authors.forename: David C
authors.initials: DC
authors.lastname: Mikles
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Deegan
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Seldeen
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Bates
authors.forename: Amjad
authors.initials: A
authors.lastname: Farooq
mesh_terms: D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D013816:Thermodynamics; D051020:bcl-X Protein / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C494811:BCL2L1 protein, human; D008024:Ligands; D008565:Membrane Proteins; D051020:bcl-X Protein