The structures of recombinant wild-type human acetylcholinesterase and of its E202Q mutant, as complexes with fasciculin-II, a `three-finger' snake neurotoxin, have been determined to 2.8 and 2.7 Å resolution, respectively. The overall structures of these complexes are similar to those of the Torpedo and mouse enzymes with fasciculin-II. Comparison of the wild-type and the mutant structures shows that removal of the charged group from the protein core, and its substitution by a neutral isosteric moiety, does not disrupt the functional architecture of the active center.