title: Helix orientations in membrane-associated Bcl-X(L) determined by 15N-solid-state NMR spectroscopy.
abstract: Controlled cell death is fundamental to tissue hemostasis and apoptosis malfunctions can lead to a wide range of diseases. Bcl-x(L) is an anti-apoptotic protein the function of which is linked to its reversible interaction with mitochondrial outer membranes. Its interfacial and intermittent bilayer association makes prediction of its bound structure difficult without using methods able to extract data from dynamic systems. Here we investigate Bcl-x(L) associated with oriented lipid bilayers at physiological pH using solid-state NMR spectroscopy. The data are consistent with a C-terminal transmembrane anchoring sequence and an average alignment of the remaining helices, i.e. including helices 5 and 6, approximately parallel to the membrane surface. Data from several biophysical approaches confirm that after removal of the C-terminus from Bcl-x(L) its membrane interactions are weak. In the presence of membranes Bcl-x(L) can still interact with a Bak BH3 domain peptide suggesting a model where the hydrophobic C-terminus of the protein unfolds and inserts into the membrane. During this conformational change the Bcl-x(L) hydrophobic binding pocket becomes accessible for protein-protein interactions whilst the structure of the N-terminal region remains intact.
authors.affiliation: Institut de Chimie de Strasbourg, Université Louis Pasteur/CNRS LC3-UMR 7177, 4 rue Blaise Pascal, 67070 Strasbourg, France.
authors.forename: Christopher
authors.initials: C
authors.lastname: Aisenbrey
authors.forename: U S
authors.initials: US
authors.lastname: Sudheendra
authors.forename: Helen
authors.initials: H
authors.lastname: Ridley
authors.forename: Philippe
authors.initials: P
authors.lastname: Bertani
authors.forename: Arnaud
authors.initials: A
authors.lastname: Marquette
authors.forename: Svetlana
authors.initials: S
authors.lastname: Nedelkina
authors.forename: Jeremy H
authors.initials: JH
authors.lastname: Lakey
authors.forename: Burkhard
authors.initials: B
authors.lastname: Bechinger
mesh_terms: D003198:Computer Simulation; D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008560:Membrane Fluidity; D008956:Models, Chemical; D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000032:analysis / Q000737:chemistry; D011487:Protein Conformation; D051020:bcl-X Protein / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D008051:Lipid Bilayers; D009587:Nitrogen Isotopes; D051020:bcl-X Protein