title: Targeting of Bcl-2 to the mitochondrial outer membrane by a COOH-terminal signal anchor sequence.
abstract: The protooncogene product Bcl-2 is an integral membrane protein that functions as a suppressor of programmed cell death. It contains a single predicted transmembrane segment located at its COOH terminus. Here, we show that the transmembrane domain of human Bcl-2 functions as a mitochondrial signal anchor sequence that targets and inserts the protein into the outer membrane in an Ncyto-C(in) orientation, leaving the bulk of the polypeptide facing the cytosol. Deletion of the COOH-terminal 22 amino acids of Bcl-2 abrogated protein targeting, whereas fusion of this domain to the COOH terminus of dihydrofolate reductase resulted in targeting and insertion of the hybrid protein into the outer membrane in a manner similar to that of Bcl-2. The sequence of the hydrophobic core of the Bcl-2 signal anchor is similar to the corresponding region of the NH2-terminal signal anchor of the mitochondrial outer membrane protein in yeast, Mas70p. A synthetic peptide comprising the Mas70p signal anchor sequence effectively competed for insertion of Bcl-2 into the outer membrane but had no effect on the comparatively low association that Bcl-2 makes with endoplasmic reticulum microsomes. Insertion of Bcl-2 into the mitochondrial outer membrane is mechanistically different than its association with microsomes.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Nguyen
authors.forename: D G
authors.initials: DG
authors.lastname: Millar
authors.forename: V W
authors.initials: VW
authors.lastname: Yong
authors.forename: S J
authors.initials: SJ
authors.lastname: Korsmeyer
authors.forename: G C
authors.initials: GC
authors.lastname: Shore
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D005656:Fungal Proteins / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D007700:Kinetics; D008223:Lymphoma; D008565:Membrane Proteins / Q000096:biosynthesis; D008928:Mitochondria / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D011519:Proto-Oncogenes; D051381:Rats; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D014407:Tumor Cells, Cultured
chemical_list: D005656:Fungal Proteins; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D021382:Protein Sorting Signals; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011956:Receptors, Cell Surface; D029701:Saccharomyces cerevisiae Proteins; C489039:TOM70 protein, S cerevisiae; D011505:Protein-Tyrosine Kinases