SNAREs in Opposing Bilayers Interact in a Circular Array to Form Conducting Pores
Sang-Joon Cho, Marie Kelly, Katherine T. Rognlien, Jin Ah Cho, J. K. Heinrich Hörber, and Bhanu P. Jena
Departments of Physiology and Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201 USA
The process of fusion at the nerve terminal is mediated via a specialized set of proteins in the synaptic vesicles and the presynaptic membrane. Three soluble N-ethylmaleimide-sensitive factor (NSF)-attachment protein receptors (SNAREs) have been implicated in membrane fusion. The structure and arrangement of these SNAREs associated with lipid bilayers were examined using atomic force microscopy. A bilayer electrophysiological setup allowed for measurements of membrane conductance and capacitance. Here we demonstrate that the interaction of these proteins to form a fusion pore is dependent on the presence of t-SNAREs and v-SNARE in opposing bilayers. Addition of purified recombinant v-SNARE to a t-SNARE-reconstituted lipid membrane increased only the size of the globular t-SNARE oligomer without influencing the electrical properties of the membrane. However when t-SNARE vesicles were added to a v-SNARE membrane, SNAREs assembles in a ring pattern and a stepwise increase in capacitance, and increase in conductance were observed. Thus, t- and v-SNAREs are required to reside in opposing bilayers to allow appropriate t-/v-SNARE interactions leading to membrane fusion.
Biophys J, November 2002, p. 2522-2527, Vol. 83, No. 5