Neuronal SNAREs do not trigger fusion between synthetic membranes but do promote PEG-mediated membrane fusion
Neuronal SNAREs do not trigger fusion between synthetic membranes but do promote PEG-mediated membrane fusion
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DOI：
10.1529/biophysj.105.069617
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发表时间：
2006-03-01
影响因子：
3.4
通讯作者：
Lentz, BR
中科院分区：
文献类型：
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作者：
Dennison, SM;Bowen, ME;Lentz, BR
在允许形成不渗透膜的低表面浓度下，当囊泡被低浓度的聚乙二醇（PEG）接触时，神经元可溶性n -乙基马来酰亚胺敏感因子附着蛋白受体（SNARE）蛋白形成稳定的，平行的，反式复合物。令人惊讶的是，在这些条件下，形成稳定的SNARE复合物并不会引发核聚变。然而，当被较高浓度的PEG触发时，神经元SNAREs确实在低蛋白/脂质比下促进融合。促进peg触发的融合需要磷脂酰丝氨酸，并且仅依赖于SNAREs的表面浓度，而不依赖于trans SNARE复合物的形成。这些结果是在突触囊泡中突触brevin的蛋白质表面浓度和最佳的促聚变脂质组成下获得的。在蛋白/脂质比更高的情况下，在没有PEG的情况下，由SNARE复合物连接的囊泡在37℃下缓慢地混合脂质，这与早期的报道一致。然而，含有高蛋白/脂质比（>= 1:250）syntaxin的囊泡失去了膜的完整性。我们得出的结论是，神经元SNARE复合体通过连接膜来促进融合，而syntaxin和synaptobrevin蛋白会破坏膜，从而有利于茎复合体的形成，并促进茎向融合孔的转化。这些作用类似于病毒融合肽和跨膜结构域的作用，但它们本身并不足以在我们的体外系统中产生突触囊泡中记录的表面浓度的融合。因此，很可能是SNARE复合体以外的蛋白质或因子触发了体内的融合。
At low surface concentrations that permit formation of impermeable membranes, neuronal soluble N-ethyl maleimide sensitive factor attachment protein receptor (SNARE) proteins form a stable, parallel, trans complex when vesicles are brought into contact by a low concentration of poly(ethylene glycol) (PEG). Surprisingly, formation of a stable SNARE complex does not trigger fusion under these conditions. However, neuronal SNAREs do promote fusion at low protein/lipid ratios when triggered by higher concentrations of PEG. Promotion of PEG-triggered fusion required phosphatidylserine and depended only on the surface concentration of SNAREs and not on the formation of a trans SNARE complex. These results were obtained at protein surface concentrations reported for synaptobrevin in synaptic vesicles and with an optimally fusogenic lipid composition. At a much higher protein/lipid ratio, vesicles joined by SNARE complex slowly mixed lipids at 37 degrees C in the absence of PEG, in agreement with earlier reports. However, vesicles containing syntaxin at a high protein/lipid ratio (>= 1:250) lost membrane integrity. We conclude that the neuronal SNARE complex promotes fusion by joining membranes and that the individual proteins syntaxin and synaptobrevin disrupt membranes so as to favor formation of a stalk complex and to promote conversion of the stalk to a fusion pore. These effects are similar to the effects of viral fusion peptides and transmembrane domains, but they are not sufficient by themselves to produce fusion in our in vitro system at surface concentrations documented to occur in synaptic vesicles. Thus, it is likely that proteins or factors other than the SNARE complex must trigger fusion in vivo.