Munc18-2/syntaxin3 complexes are spatially separated from syntaxin3-containing SNARE complexes.
Exocytosis of mast cell granules requires a vesicular- and plasma membrane-associated fusion machinery. We examined the distribution of SNARE membrane fusion and Munc18 accessory proteins in lipid rafts of RBL mast cells. SNAREs were found either excluded (syntaxin2), equally distributed between raft and non-raft fractions (syntaxin4, VAMP-8, VAMP-2), or selectively enriched in rafts (syntaxin3, SNAP-23). Syntaxin4-binding Munc18-3 was absent, whereas small amounts of the syntaxin3-interacting partner Munc18-2 consistently distributed into rafts. Cognate SNARE complexes of syntaxin3 with SNAP-23 and VAMP-8 were enriched in rafts, whereas Munc18-2/syntaxin3 complexes were excluded. This demonstrates a spatial separation between these two types of complexes and suggests that Munc18-2 acts in a step different from SNARE complex formation and fusion.
Pombo
Isabel
I
Unité d'Immuno-Allergie, Institut Pasteur, Paris, France.
Rivera
Juan
J
Blank
Ulrich
U
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D046911:Macromolecular Substances; D008407:Mast Cells / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins / Q000378:metabolism; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism*; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism; D015203:Reproducibility of Results; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D011506:Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D017455:Receptors, IgE; C100493:SNAP23 protein, human; D050600:SNARE Proteins; C497942:Stxbp2 protein, rat; C491830:Vamp8 protein, rat; D033921:Vesicular Transport Proteins