title: Conformation of membrane-associated proapoptotic tBid.
abstract: The proapoptotic Bcl-2 family protein Bid is cleaved by caspase-8 to release the C-terminal fragment tBid, which translocates to the outer mitochondrial membrane and induces massive cytochrome c release and cell death. In this study, we have characterized the conformation of tBid in lipid membrane environments, using NMR and CD spectroscopy with lipid micelle and lipid bilayer samples. In micelles, tBid adopts a unique helical conformation, and the solution NMR (1)H/(15)N HSQC spectra have a single well resolved resonance for each of the protein amide sites. In lipid bilayers, tBid associates with the membrane with its helices parallel to the membrane surface and without trans-membrane helix insertion, and the solid-state NMR (1)H/(15)N polarization inversion with spin exchange at the magic angle spectrum has all of the amide resonances centered at (15)N chemical shift (70-90 ppm) and (1)H-(15)N dipolar coupling (0-5 kHz) frequencies associated with NH bonds parallel to the bilayer surface, with no intensity at frequencies associated with NH bonds in trans-membrane helices. Thus, the cytotoxic activity of tBid at mitochondria may be similar to that observed for antibiotic polypeptides, which bind to the surface of bacterial membranes as amphipathic helices and destabilize the bilayer structure, promoting the leakage of cell contents.
authors.affiliation: Burnham Institute, La Jolla, California 92037, USA.
authors.forename: Xiao-Min
authors.initials: XM
authors.lastname: Gong
authors.forename: Jungyuen
authors.initials: J
authors.lastname: Choi
authors.forename: Carla M
authors.initials: CM
authors.lastname: Franzin
authors.forename: Dayong
authors.initials: D
authors.lastname: Zhai
authors.forename: John C
authors.initials: JC
authors.lastname: Reed
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Marassi
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008823:Micelles; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein
chemical_list: C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D008051:Lipid Bilayers; D008823:Micelles; D010446:Peptide Fragments; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein