The Snare Motif of Membrane-Anchored Synaptobrevin Exhibits an Aqueous-Interfacial Partitioning that is Modulated by Membrane Curvature

Abstract

The SNARE forming motif of the vesicle associated protein synaptobrevin 2, is generally thought to be unstructured in the aqueous phase prior to assembly of the neuronal core SNARE complex. Here, the structure and interfacial association of the full-length vesicle SNARE, synaptobrevin, was compared in four different lipid environments using NMR and EPR spectroscopy. In micelles, segments of the SNARE motif are helical and associated with the interface. However, the fraction of helix and interfacial association decreases as synaptobrevin is moved from micelle to bicelle to bilayer environments, suggesting that the tendency towards interfacial association is sensitive to membrane curvature. In bilayers, the SNARE motif of synaptobrevin transiently associates with the lipid interface, and regions that are helical in micelles are in conformational and environmental exchange in bicelles and bilayers. This work demonstrates that the SNARE motif of synaptobrevin has a significant propensity to form a helix and exchange with the membrane interface prior to SNARE assembly. This transient interfacial association and its sensitivity to membrane curvature and/or defects likely play a role in SNARE recognition events that drive membrane fusion.