title: SNAP-24, a Drosophila SNAP-25 homologue on granule membranes, is a putative mediator of secretion and granule-granule fusion in salivary glands.
abstract: Fusion of vesicles with target membranes is dependent on the interaction of target (t) and vesicle (v) SNARE (soluble NSF (N-ethylmaleimide-sensitive fusion protein) attachment protein receptor) proteins located on opposing membranes. For fusion at the plasma membrane, the t-SNARE SNAP-25 is essential. In Drosophila, the only known SNAP-25 isoform is specific to neuronal axons and synapses and additional t-SNAREs must exist that mediate both non-synaptic fusion in neurons and constitutive and regulated fusion in other cells. Here we report the identification and characterization of SNAP-24, a closely related Drosophila SNAP-25 homologue, that is expressed throughout development. The spatial distribution of SNAP-24 in the nervous system is punctate and, unlike SNAP-25, is not concentrated in synaptic regions. In vitro studies, however, show that SNAP-24 can form core complexes with syntaxin and both synaptic and non-synaptic v-SNAREs. High levels of SNAP-24 are found in larval salivary glands, where SNAP-24 localizes mainly to granule membranes rather than the plasma membrane. During glue secretion, the massive exocytotic event of these glands, SNAP-24 containing granules fuse with one another and the apical membrane, suggesting that glue secretion utilizes compound exocytosis and that SNAP-24 mediates secretion.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford Medical School, Stanford, CA 94305, USA. barbara.niemeyer@med-rz.uni-saarland.de
authors.forename: B A
authors.initials: BA
authors.lastname: Niemeyer
authors.forename: T L
authors.initials: TL
authors.lastname: Schwarz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002874:Chromosome Mapping; D003594:Cytoplasmic Granules / Q000502:physiology* / Q000648:ultrastructure; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D004625:Embryo, Nonmammalian; D018507:Gene Expression Regulation, Developmental; D007425:Intracellular Membranes / Q000502:physiology / Q000648:ultrastructure; D007814:Larva; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011679:Pupa; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012469:Salivary Glands / Q000502:physiology* / Q000648:ultrastructure; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure; D050825:Synaptosomal-Associated Protein 25
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; C494206:Snap24 protein, Drosophila; C494207:Snap25 protein, Drosophila; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D050825:Synaptosomal-Associated Protein 25