Novel secretory vesicle proteins essential for membrane fusion display extracellular-matrix domains.
Exocytotic mutants can be obtained in Paramecium that affect the organization of the fusion machinery, visible by electron microscopy. The site of action of the genes in the plasma membrane, cytosol or secretory compartment can easily be determined in such mutants. Functional complementation cloning of exocytotic mutants specifically affected in the secretory compartment, nd2-1 and nd169-1, reported here, and the previously studied nd7-1, led to the discovery of a set of novel proteins that display PSI and EGF domains, normally found in extracellular matrix proteins and involved in transmembrane signaling. The structure of one of these proteins, Nd2p, and of the product of a paralog found in the genome Nd22p, corresponds to that of type I membrane receptors, generally involved in protein and vesicle sorting. Our characterization suggests that the proteins we have identified are required to indicate the presence of a mature secretory vesicle to the plasma membrane, to prepare the machinery for fusion. We propose to name this novel subclass of receptors VEMIF, for Vesicular Extracellular-Matrix-like proteins Involved in preparing membrane Fusion.
Froissard
Marine
M
Centre de Génétique Moléulaire, Centre National de la Recherche Scientifique, Avenue de la Terrasse, 91198 Gif-sur-Yvette cedex, France.
Keller
Anne-Marie
AM
Dedieu
Jean-Claude
JC
Cohen
Jean
J
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D002462:Cell Membrane / Q000378:metabolism*; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism; D005089:Exocytosis; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism*; D005614:Freeze Fracturing; D020868:Gene Silencing; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D009841:Oligonucleotides / Q000737:chemistry; D010247:Paramecium / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000502:physiology; D012313:RNA / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction
D008565:Membrane Proteins; C107339:ND7 protein, Protozoa; D009841:Oligonucleotides; D015800:Protozoan Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004815:Epidermal Growth Factor; D012313:RNA