αC-Conotoxin PrXA (AlphaC-PrXA) was originally isolated from the venom of the fish-hunting Conus parius. αC-Conotoxin PrXA is a highly specific inhibitor of the neuromuscular nAChR. It potently antagonizes mouse muscle ***** α1/β1/ε/δ nAChR subunits (IC50 = 1.8 nM) as well as fetal mouse muscle α1/β1/γ/δ nAChR subunits (IC50 = 3 nM). αC-Conotoxin PrXA competes with α-bungarotoxin for binding at the α/δ and α/γ nAChR subunit interfaces (with higher affinity however for the α/δ subunit interface). The 3D structure of αC-Conotoxin PrXA is different from other conotoxins that target nAChR and it is most similar to Waglerin-1, a nAChR blocker isolated from a snake venom. αC-Conotoxin PrXA is a useful tool for investigating the structure and physiological role of nAChRs.