1VOT:
reference: Structure of acetylcholinesterase complexed with the nootropic alkaloid, (-)-huperzine A., Raves ML, Harel M, Pang YP, Silman I, Kozikowski AP, Sussman JL, Nat Struct Biol. 1997 Jan;4(1):57-63. PMID: 8989325

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).