In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: MuSK acts with rapsyn to colocalize receptors for this molecule when it binds to the proteoglycan agrin found in the basal lamina. Binding of this molecule to those receptors causes a rotation of five transmembrane M2 helices. Alpha-bungarotoxin blocks the activity of this molecule, which is broken down by a namesake esterase rather than reuptaken in the synaptic cleft. The enzyme that catalyzes this molecule's synthesis is at abnormally low concentrations in Alzheimer's patients. Black widow venom stimulates excess release of this molecule, while botulinum toxin blocks its release; both result in paralysis. For 10 points, name this molecule found at the neuromuscular junction.
A:
Science