| Species | Original | Mutated to | Mutation |
| Human | Ile 84 |
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| Rat Equivalent | Ile 83 |
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| Mouse Equivalent | Ile 89 |
Ala | I89A |
Nine residues (Thr 86, Thr 87, Tyr 88, Ile 89, Tyr 91, Arg 92, Gln 93, Tyr 94, Trp 95) were mutated individually to alanine (alanine scanning mutagenesis. The ligands [3H]granisetron, curare, and serotonin were used to examine the properites of the 5-HT3 binding site.
W90F was analyzed instead of W90A, and it proved to be the only one that significantly affected the interaction of curare with the receptor. R92A was the only substitution that altered the affinity of the agonist serotonin. W90F, R92A, and Y94A all reduced the affinity of [3H] ganisetron. The periodicity of this effect suggests the involvement of a beta-strand.