BPS2026 – Cholesterol-containing membranes decrease the helicity of the SNARE protein SNARE SNAP-25

Neurotransmitter release in neurons requires membrane fusion between synaptic vesicles and the presynaptic membrane. Lipids in both membranes merge through the action of SNARE proteins including SNAP-25. Changes in SNAP-25 structure or lipid composition likely modify this process. SNAP-25 has two isoforms, SNAP-25A (25A) and SNAP-25B (25B), the expression patterns of these isoforms vary throughout different brain regions and neuronal developmental stages. In vivo SNAP-25 anchors to the presynaptic membrane via attachment of palmitic acid to at least one of the four cysteines. Here, we show mixing SNAP-25 (not palmitoylated) with liposomes alters both protein structure and lipid properties. Using circular dichroism (CD), we measured changes in secondary structure of SNAP-25 when mixed with liposomes made from DPPC, DPPC + cholesterol, and POPC. Some lipids induced structural changes in SNAP-25 that were isoform-dependent, consistent with a direct lipid-protein interaction. This protein-lipid interaction was confirmed by a shift in the DPPC melting temperature measured by differential scanning calorimetry (DSC). We hypothesize that neurons select the isoform and/or lipid composition ideal for the various forms of synaptic transmission.