Adrenal chromaffin cells contain functionally different SNAP-25 monomers and SNAP-25/syntaxin heterodimers.
Syntaxin and SNAP-25 (synaptosome-associated protein of 25 kDa), associated with the neuronal plasmalemma, and synaptobrevin, a membrane protein of synaptic vesicles, are essential components of the exocytotic apparatus of synaptic vesicles. All three can be proteolytically cleaved by tetanus and/or botulinum neurotoxins. As a consequence of their cleavage, exocytosis of neurotransmitters is blocked. In adrenal chromaffin cells botulinum neurotoxin A only incompletely inhibits exocytosis. This incomplete inhibition of exocytosis is associated with only partial cleavage of SNAP-25 by the toxin, indicating that distinct pools of SNAP-25 may exist in chromaffin cells which differ in their sensitivities to botulinum neurotoxin A. In line with this result we localized SNAP-25 by immunogold electron microscopy not only to the plasmalemma but also to the chromaffin vesicle membrane. Moreover, in addition to SNAP-25 monomers, stable SNAP-25/syntaxin heterodimers were found in chromaffin cells. Subfractionation studies revealed the presence of SNAP-25/syntaxin heterodimers in an enriched fraction of chromaffin vesicles. This complex proved to be stable in SDS, and SNAP-25 within heterodimers was resistant to proteolytic attack by botulinum neurotoxin A. We suggest that these preexisting heterodimers may serve as receptors of soluble NSF attachment proteins (SNAP receptors) during chromaffin vesicle exocytosis.
Höhne-Zell
B
B
Anatomisches Institut der Technischen Universität München, Munich, Germany.
Gratzl
M
M
D000311:Adrenal Glands / Q000737:chemistry; D000818:Animals; D001426:Bacterial Proteins; D019274:Botulinum Toxins, Type A / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000737:chemistry; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D019439:Chromaffin Cells / Q000737:chemistry* / Q000648:ultrastructure; D002837:Chromaffin Granules / Q000737:chemistry* / Q000648:ultrastructure; D019281:Dimerization; D005089:Exocytosis / Q000187:drug effects; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000737:chemistry; D008565:Membrane Proteins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013301:Streptolysins / Q000494:pharmacology; D050825:Synaptosomal-Associated Protein 25
D001426:Bacterial Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D013301:Streptolysins; D050825:Synaptosomal-Associated Protein 25; C025964:streptolysin O; D012967:Sodium Dodecyl Sulfate; D019274:Botulinum Toxins, Type A; D009638:Norepinephrine