Docking of liposomes to planar surfaces mediated by trans-SNARE complexes

Author :Olga Vites, Ernst-Ludwig Florin, and Reinhard Jahn
Publication :Biophys. J.
Volume :95
Number :(3)
Pages :1295-1302
Year :2008

ABSTRACT Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) 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 assemble in a zipperlike
fashion, pulling the membranes together and initiating fusion. However, it is not clear to what extent SNARE assembly
contributes to membrane attachment and membrane fusion. Using the neuronal SNAREs synaptobrevin (VAMP), SNAP-25, and
syntaxin as examples, we show here that liposomes containing synaptobrevin firmly attach to planar surfaces containing
immobilized syntaxin. Attachment requires the formation of SNARE complexes because it is dependent on the presence of SNAP-
25. Binding is competed for by soluble SNARE fragments, with noncognate SNAREs such as endobrevin (VAMP8), VAMP4, and
VAMP7 (Ti-VAMP) being effective but less potent in some cases. Furthermore, although SNAP-23 is unable to substitute for
SNAP-25 in the attachment assay, 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.