The synaptophysin/synaptobrevin complex dissociates independently of neuroexocytosis

Abstract

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 a-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.

GSK-3β Inhibits Presynaptic Vesicle Exocytosis by Phosphorylating P/Q-Type Calcium Channel and Interrupting SNARE Complex Formation

“…These data suggest that Syb must dissociate from SypI before entering the SNARE complex for the exocytosis. Elevation of intracellular Ca 2ϩ causes dissociation of the Syb-SypI complex (Reisinger et al, 2004). Our data in the present study show that activation of GSK-3 retards the dissociation of Syb-SypI complex, which is consistent with a previous study showing that suppressing GSK-3 activity in zebrafish retinal ganglion cell increases the size of Syb-positive puncta in axons terminal (Tokuoka et al, 2002).…”

“…The resulting supernatant was further centrifuged at 20,000 ϫ g for 15 min at 4°C, and P2 fraction containing synaptosome was collected. Synaptosomes (0.5 mg of protein) were incubated with streptolysin O to permeabilize the plasma membrane following the administration of DMSO, wortmannin (Wort), Wort plus SB216763 (SB), and SB alone for 30 min at 37°C (Reisinger et al, 2004). After adding the anti-SypI or anti-Syb antibody to the synaptosome, the reaction mixture was gently rocked at 4°C overnight.…”

Taipoxin Induces Synaptic Vesicle Exocytosis and Disrupts the Interaction of Synaptophysin I with VAMP2

“…This may be taken as an indication that the disruption of the SypI-VAMP2 interaction by Tpx precedes the enhancement of exocytotic fusion and the subsequent inhibition of endocytosis, which lead to swelling of the terminals. Although our data, obtained in live neurons, do not formally prove that disruption of the SypI/VAMP2 interaction and enhancement of exocytosis induced by Tpx are mechanistically connected, they are in keeping with previous in vitro studies (Calakos and Scheller, 1994;Edelmann et al, 1995;Washbourne et al, 1995;Reisinger et al, 2004) supporting the modulatory role of the SypI/VAMP2 complex at synapses. Release of VAMP2 from SypI seems to precede fusion and might be a prerequisite to make SVs competent for exocytosis (see also Reisinger et al, 2004).…”

“…Although our data, obtained in live neurons, do not formally prove that disruption of the SypI/VAMP2 interaction and enhancement of exocytosis induced by Tpx are mechanistically connected, they are in keeping with previous in vitro studies (Calakos and Scheller, 1994;Edelmann et al, 1995;Washbourne et al, 1995;Reisinger et al, 2004) supporting the modulatory role of the SypI/VAMP2 complex at synapses. Release of VAMP2 from SypI seems to precede fusion and might be a prerequisite to make SVs competent for exocytosis (see also Reisinger et al, 2004). However, disruption of the SypI/VAMP2 interaction by Tpx is not sufficient per se to promote SV exocytosis, because it was also observed in those terminals in which SV had not undergone massive fusion (i.e., the small synaptic boutons).…”

Comparison the Effect of Zinc Oxide and Magnesium Oxide Nano Particles on Long Term Memory in Adult Male Mice

“…Increase of brain magnesium can lead to increas in selective expression of some subunits of NMDA receptor [22,26] also induction of LTP in synaps of perforant -dentate gyrus pathway and synaps of Shaffer clusters in CA1 area is depend on NMDA glutamateric receptors [26][27][28]. In CA1 area, NMDA receptor has an important role in regulation of synaptic plasticity, learning and memeory process [1,28].…”