The SNARE complex and the brake on it

A muscle contracts when a nerve ending releases acetylcholine, and that release needs three proteins to zip together: SNAP-25, syntaxin and synaptobrevin. Zipped, they pull the vesicle against the membrane until it fuses and empties. SNAP-8 copies the end of SNAP-25, so it competes for a place in that zip and makes the finished complex slower to form and less stable. Less signal released means a slightly softer pull on the muscle fibre underneath a crease.