The synaptophysin/synaptobrevin complex dissociates independently of neuroexocytosis.
Synaptophysin is one of the most abundant membrane proteins of small synaptic vesicles. In mature nerve terminals it forms a complex with the vesicular membrane protein synaptobrevin, which appears to modulate synaptobrevin's interaction with the plasma membrane-associated proteins syntaxin and SNAP25 to form the SNARE complex as a prerequisite for membrane fusion. Here we show that synaptobrevin is preferentially cleaved by tetanus toxin while bound to synaptophysin or when existing as a homodimer. The synaptophysin/synaptobrevin complex is, however, not affected when neuronal secretion is blocked by botulinum A toxin which cleaves SNAP25. Excessive stimulation with alpha-latrotoxin or Ca(2+)-ionophores dissociates the synaptophysin/synaptobrevin complex and increases the interaction of the other SNARE proteins. The stimulation-induced dissociation of the synaptophysin/synaptobrevin complex is not inhibited by pre-incubating neurones with botulinum A toxin, but depends on extracellular calcium. However, the synaptophysin/synaptobrevin complex cannot be directly dissociated by calcium alone or in combination with magnesium. The dissociation of synaptobrevin from synaptophysin appears to precede its interaction with the other SNARE proteins and does not depend on the final fusion event. This finding further supports the modulatory role the synaptophysin/synaptobrevin complex may play in mature neurones.
Reisinger
Clemens
C
Centrum für Anatomie, Charité Universitätsmedizin, Berlin, AG Funktionelle Zellbiologie, Berlin, Germany.
Yelamanchili
Sowmya V
SV
Hinz
Britta
B
Mitter
Diana
D
Becher
Anja
A
Bigalke
Hans
H
Ahnert-Hilger
Gudrun
G
D000818:Animals; D019274:Botulinum Toxins, Type A / Q000494:pharmacology; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D019281:Dimerization; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology; D007476:Ionophores / Q000494:pharmacology; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008565:Membrane Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D050683:R-SNARE Proteins; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology; D013268:Stimulation, Chemical; D016708:Synaptophysin / Q000737:chemistry / Q000378:metabolism*; D050825:Synaptosomal-Associated Protein 25; D013574:Synaptosomes / Q000737:chemistry / Q000187:drug effects; D013744:Tetanus Toxin / Q000737:chemistry / Q000494:pharmacology
D007476:Ionophores; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; C494209:Snap25 protein, mouse; C494210:Snap25 protein, rat; D013111:Spider Venoms; D016708:Synaptophysin; D050825:Synaptosomal-Associated Protein 25; D013744:Tetanus Toxin; C020763:alpha-latrotoxin; D019274:Botulinum Toxins, Type A; D008274:Magnesium; D002118:Calcium