title: SNAP-23 and syntaxin-2 localize to the extracellular surface of the platelet plasma membrane.
abstract: SNARE proteins direct membrane fusion events required for platelet granule secretion. These proteins are oriented in cell membranes such that most of the protein resides in a cytosolic compartment. Evaluation of SNARE protein localization in activated platelets using immunonanogold staining and electron microscopy, however, demonstrated expression of SNAP-23 and syntaxin-2 on the extracellular surface of the platelet plasma membrane. Flow cytometry of intact platelets confirmed trypsin-sensitive SNAP-23 and syntaxin-2 localization to the extracellular surface of the plasma membrane. Acyl-protein thioesterase 1 and botulinum toxin C light chain released SNAP-23 and syntaxin-2, respectively, from the surface of intact platelets. When resting platelets were incubated with both acyl-protein thioesterase 1 and botulinum toxin C light chain, a complex that included both SNAP-23 and syntaxin-2 was detected in supernatants, indicating that extracellular SNARE proteins retain their ability to bind one another. These observations represent the first description of SNARE proteins on the extracellular surface of a cell.
authors.affiliation: Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA. rflaumen@bidmc.harvard.edu
authors.forename: Robert
authors.initials: R
authors.lastname: Flaumenhaft
authors.forename: Nataliya
authors.initials: N
authors.lastname: Rozenvayn
authors.forename: Dian
authors.initials: D
authors.lastname: Feng
authors.forename: Ann M
authors.initials: AM
authors.lastname: Dvorak
mesh_terms: D001792:Blood Platelets / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D001905:Botulinum Toxins / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D046529:Microscopy, Electron, Transmission; D010170:Palmitoyl-CoA Hydrolase / Q000737:chemistry; D015539:Platelet Activation / Q000502:physiology*; D050766:Qb-SNARE Proteins / Q000096:biosynthesis* / Q000737:chemistry; D050767:Qc-SNARE Proteins / Q000096:biosynthesis* / Q000737:chemistry; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism; D050827:Syntaxin 1 / Q000096:biosynthesis* / Q000737:chemistry
chemical_list: D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human; C074558:STX2 protein, human; D050827:Syntaxin 1; D010170:Palmitoyl-CoA Hydrolase; D001905:Botulinum Toxins; C096324:botulinum toxin type C