Investigating Complexin-Membrane Interactions Using NMR and Optical Methods.

Complexins are a family of small presynaptic proteins that regulate neurotransmitter release at nerve terminals and are highly conserved in evolution. While direct interactions with SNARE proteins are critical for all complexin functions, binding of their disordered C-terminal domains (CTD) to membranes, especially to synaptic vesicle membranes, is essential for the ability of complexin to inhibit vesicle release. Furthermore, while some complexin CTDs possess an endogenous affinity for membranes, other complexin isoforms are subject to lipidation at their C-termini, which is presumed to confer additional membrane binding. Therefore, an in depth understanding of complexin-membrane interactions is required to elucidate the mechanistic basis for their inhibitory activity. Here we describe protocols for characterizing complexin-membrane interactions using solution state nuclear magnetic resonance (NMR) spectroscopy as well as single molecule total-internal reflection fluorescence (TIRF) methods, along with protocols for generating isotopically labeled samples of unmodified and farnesylated complexins and for characterizing synthetic lipid vesicles using dynamic light scattering (DLS).