Docking of liposomes to planar surfaces mediated by trans-SNARE complexes
Olga Vites 1, Ernst-Ludwig Florin 2 and Reinhard Jahn 3*
1 London Research Institute
2 University of Texas at Austin
3 Max-Planck-Inst Biophysical Chem
* To whom correspondence should be addressed. E-mail: rjahn{at}gwdg.de.
Submitted on January 15, 2008
Revised on February 7, 2008
Accepted on 1 April 2008
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Abstract |
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SNARE proteins play a key role in membrane fusion in the secretory pathway. In vitro, SNAREs spontaneously assemble into helical SNARE complexes with the transmembrane domains at the C-terminal end. During fusion, SNAREs are thought to bridge the two membranes and to assemble in a zipper-like fashion, pulling the membranes together and initiating fusion. However, it is not clear to which extent SNARE assembly contributes to membrane attachment and membrane fusion. Using the neuronal SNAREs synaptobrevin (VAMP), SNAP-25, and syntaxin as example, we show here that liposomes containing synaptobrevin firmly attach to planar surfaces containing immobilized syntaxin. Attachment requires formation of SNARE complexes as it is dependent on the presence of SNAP-25. Binding is competed for by soluble SNARE fragments, with non-cognate SNAREs such as endobrevin (VAMP8), VAMP4, and VAMP7 (Ti-VAMP) being effective but less potent in some cases. Furthermore, SNAP-23 is unable to substitute for SNAP-25 in the attachment assay although it forms complexes of comparable stability and is capable of substituting in liposome fusion assays. Vesicle attachment is initiated by SNARE assembly at the N-terminal end of the helix bundle. We conclude that SNAREs can indeed form stable trans-complexes that result in vesicle attachment if progression to fusion is prevented, further supporting the zipper model of SNARE function.
Key Words:
SNAP-25, SNAREs, docking, liposomes, synaptobrevin, syntaxin
