title: Helix 6 of tBid is necessary but not sufficient for mitochondrial binding activity.
abstract: The apoptosis effector Bid regulates cell death at the level of mitochondrial cytochrome c efflux. Bid consists of 8 alpha-helices (designated H1 through H8, respectively) and is a soluble cytosolic protein in its native state. Proteolysis of the N-terminus (encompassing H1 and H2) of Bid yields activated "tBid" (truncated Bid), which translocates to the mitochondria and induces the efflux of cytochrome c. Here, we demonstrate that helix H6 of tBid is necessary, albeit not sufficient, for mitochondrial binding. In particular, a 33 amino acid long domain, which encompassed H6 and H7, behaved as the minimum domain in tBid that was sufficient for mitochondrial binding. Unexpectedly, the hydrophobic surface of these helices could be mutated without altering the binding activity of the domain, implying that the secondary structure of the helices may be the key determinant of binding. These experiments expand our mechanistic understanding of the apoptotic regulator, tBid.
authors.affiliation: Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA.
authors.forename: X
authors.initials: X
authors.lastname: Hu
authors.forename: Z
authors.initials: Z
authors.lastname: Han
authors.forename: J H
authors.initials: JH
authors.lastname: Wyche
authors.forename: E A
authors.initials: EA
authors.lastname: Hendrickson
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism*; D002451:Cell Compartmentation / Q000502:physiology; D045304:Cytochromes c / Q000378:metabolism*; D005456:Fluorescent Dyes; D018922:HL-60 Cells; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D045304:Cytochromes c