Human 5-HT_3A -- Tyr 45

mTyr50Phe mTyr50Ala mTyr50Ser

Eleven residues (Tyr 50, Tyr 73, Tyr 88, Tyr 91, Tyr 94, Tyr 141, Tyr 143, Tyr 153, Tyr 167, Tyr 234, Tyr 240) were mutated individually for alanine, serine and some residues for phenylalanine. The ligands [3H]granisetron and 5-HT were used to examine the properities of ligand binding sites and function of the 5-HT3A receptor, respectively.

Mouse 5-HT3A receptors were expressed in Xenopus Oocytes (cRNA injection) and studied using two-electrode voltage-clamp technique. HEK293 cells were used in radioligand binding and calcium imaging assays to study the affinity of [3H]granisetron and the potency of 5-HT, respectively.

Mutants Y50A ,Y50F and Y50S did not bind [3H]granisetron. Surprisingly, the mutation in Y50S did not significantly affect the potency of 5-HT.

NT, Not tested ; NB, No Binding

++, Presence of cell surface receptors revealed by immunocytochemistry

-/+, Reduced cell surface receptor expression compared to WT 5-HT3A

-, Absence of cell surface receptors

* significantly different from the WT 5-HT3A receptor

Price KL, Lummis SCR (2004). The role of Tyrosine residues in the extracellular domain of the 5-Hydroxytryptamine3 receptor.The Journal of Biological Chemistry 279(22):23294-23301

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