Human 5-HT_3A -- Arg 87

mArg92Ala

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). [3H]granisetron, curare, and serotonin were used as ligands to examine the properties of the 5-HT3 binding site.

W90F was analyzed instead of W90A, and it proved to be the only mutation 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]granisetron. The periodicity of this effect suggests the participation of a beta-strand.

Yan D, Schulte MK, Bloom KE, White MM (1999) Structural Features of the Ligand-binding Domain of the Serotonin 5HT3 Receptor. The Journal of Biological Chemistry 274 (9): 5537-5541

Twenty six residues (I71, Y73,W90, R92, N128, E129, Y143, Y153, T179, T181, S182,W183, L184, W195, V201, R202, S203, S206, I207, F226, I228, D229, I230, Y234, E236, K238) thought to be within 5A of the 5-HT binding site were substituted with either alanine or a residue with somewhat similar physicochemical properties to the wildtype residue. The effects of these substitutions were investigated by measuring the binding of [3H]granisetron. The results were used to map the granisetron binding site within an homology model of the mouse 5-HT3A receptor based on the crystal structure of the AChBP. Mouse 5-HT3A receptors were expressed in HEK293 cells for radioligand binding.

The R92A (Kd=1.80 +/- 0.40 nM) mutant 5-HT3A receptor bound [3H]granisetron with a reduced affinity. The wild type receptor bound [3H]granisetron with a Kd = 0.31 +/- 0.04 nM. The R92K (Kd = 1.00 +/- 0.30 nM) mutation did not significantly alter the affinity of the [3H]granisetron binding. Lysine, like arginine is a basic residue, a positive residue appears to be required for the correct structure of the antagonist binding site.

NB, No binding

* significantly different from the WT 5-HT3A receptor

Thompson AJ, Price KL, Reeves DC, Chan SL, Chau PL, Lummis SC(2005). Locating an antagonist in the 5-HT3 receptor binding site using modeling and radioligand binding.The Journal of Biological Chemistry 280(21):20476-82

mArg92Lys

Twenty six residues (I71, Y73,W90, R92, N128, E129, Y143, Y153, T179, T181, S182,W183, L184, W195, V201, R202, S203, S206, I207, F226, I228, D229, I230, Y234, E236, K238) thought to be within 5A of the 5-HT binding site were substituted with either alanine or a residue with somewhat similar physicochemical properties to the wildtype residue. The effects of these substitutions were investigated by measuring the binding of [3H]granisetron. The results were used to map the granisetron binding site within an homology model of the mouse 5-HT3A receptor based on the crystal structure of the AChBP. Mouse 5-HT3A receptors were expressed in HEK293 cells for radioligand binding.

The R92A (Kd=1.80 +/- 0.40 nM) mutant 5-HT3A receptor bound [3H]granisteron with a reduced affinity. The wild type receptor bound [3H]granisteron with a Kd = 0.31 +/- 0.04 nM. The R92K (Kd = 1.00 +/- 0.30 nM) mutant did not significantly altered the affinity of the antagonist [3H]granisetron binding. Lysine, like Arginine is a basic residue which presumably required a positive charge for the correct structure of the antagonist binding site.

NB, No binding

* significantly different from the WT 5-HT3A receptor

Thompson AJ, Price KL, Reeves DC, Chan SL, Chau PL, Lummis SC(2005). Locating an antagonist in the 5-HT3 receptor binding site using modeling and radioligand binding.The Journal of Biological Chemistry 280(21):20476-82

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