A splice-isoform of vesicle-associated membrane protein-1 (VAMP-1) contains a mitochondrial targeting signal.
Screening of a library derived from primary human endothelial cells revealed a novel human isoform of vesicle-associated membrane protein-1 (VAMP-1), a protein involved in the targeting and/or fusion of transport vesicles to their target membrane. We have termed this novel isoform VAMP-1B and designated the previously described isoform VAMP-1A. VAMP-1B appears to be an alternatively spliced form of VAMP-1. A similar rat splice variant of VAMP-1 (also termed VAMP-1B) has recently been reported. Five different cultured cell lines, from different lineages, all contained VAMP-1B but little or no detectable VAMP-1A mRNA, as assessed by PCR. In contrast, brain mRNA contained VAMP-1A but no VAMP-1B. The VAMP-1B sequence encodes a protein identical to VAMP-1A except for the carboxy-terminal five amino acids. VAMP-1 is anchored in the vesicle membrane by a carboxy-terminal hydrophobic sequence. In VAMP-1A the hydrophobic anchor is followed by a single threonine, which is the carboxy-terminal amino acid. In VAMP-1B the predicted hydrophobic membrane anchor is shortened by four amino acids, and the hydrophobic sequence is immediately followed by three charged amino acids, arginine-arginine-aspartic acid. Transfection of human endothelial cells with epitope-tagged VAMP-1B demonstrated that VAMP-1B was targeted to mitochondria whereas VAMP-1A was localized to the plasma membrane and endosome-like structures. Analysis of C-terminal mutations of VAMP-1B demonstrated that mitochondrial targeting depends both on the addition of positive charge at the C terminus and a shortened hydrophobic membrane anchor. These data suggest that mitochondria may be integrated, at least at a mechanistic level, to the vesicular trafficking pathways that govern protein movement between other organelles of the cell.
Isenmann
S
S
Division of Human Immunology, Hanson Centre for Cancer Research, Adelaide 5000, South Australia, Australia.
Khew-Goodall
Y
Y
Gamble
J
J
Vadas
M
M
Wattenberg
B W
BW
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D050683:R-SNARE Proteins; D014407:Tumor Cells, Cultured; D014471:Umbilical Veins
D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D020033:Protein Isoforms; D050683:R-SNARE Proteins