title: Characterization of the signal that directs Bcl-x(L), but not Bcl-2, to the mitochondrial outer membrane.
abstract: It is assumed that the survival factors Bcl-2 and Bcl-x(L) are mainly functional on mitochondria and therefore must contain mitochondrial targeting sequences. Here we show, however, that only Bcl-x(L) is specifically targeted to the mitochondrial outer membrane (MOM) whereas Bcl-2 distributes on several intracellular membranes. Mitochondrial targeting of Bcl-x(L) requires the COOH-terminal transmembrane (TM) domain flanked at both ends by at least two basic amino acids. This sequence is a bona fide targeting signal for the MOM as it confers specific mitochondrial localization to soluble EGFP. The signal is present in numerous proteins known to be directed to the MOM. Bcl-2 lacks the signal and therefore localizes to several intracellular membranes. The COOH-terminal region of Bcl-2 can be converted into a targeting signal for the MOM by increasing the basicity surrounding its TM. These data define a new targeting sequence for the MOM and propose that Bcl-2 acts on several intracellular membranes whereas Bcl-x(L) specifically functions on the MOM.
authors.affiliation: Institute of Molecular Medicine and Cell Research, Albert-Ludwigs-University Freiburg, D-79106 Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kaufmann
authors.forename: Sarah
authors.initials: S
authors.lastname: Schlipf
authors.forename: Javier
authors.initials: J
authors.lastname: Sanz
authors.forename: Karin
authors.initials: K
authors.lastname: Neubert
authors.forename: Reuven
authors.initials: R
authors.lastname: Stein
authors.forename: Christoph
authors.initials: C
authors.lastname: Borner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002254:Carbonates / Q000494:pharmacology; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D008164:Luminescent Proteins / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008861:Microsomes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051381:Rats; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013347:Subcellular Fractions; D014158:Transcription, Genetic; D051020:bcl-X Protein
chemical_list: C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; C494813:Bcl2l1 protein, rat; D002254:Carbonates; D018076:DNA, Complementary; D008164:Luminescent Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D049452:Green Fluorescent Proteins; C005686:sodium carbonate