Amino acid residues involved in interaction with tyramine in the Bombyx mori tyramine receptor

To identify amino acid residues interacting with tyramine (TA) in the Bombyx mori TA (BmTA) receptor, several mutant receptors were expressed in HEK-293 cells and examined for their abilities to bind TA and to attenuate forskolin-stimulated cAMP production in response to TA. The D134A BmTA receptor showed no specific [H-3]TA binding and no TA-attenuation of cAMP levels. Although the S218A and S222A BmTA receptors showed no specific [H-3]TA binding, they still had the ability to mediate the attenuation of cAMP levels in response to the high concentration (100 mum) of TA. The double mutation of Ser218 and Ser222 to Ala, however, led to the loss of TA-attenuation of cAMP levels. The present study thus confirms that at least three amino acid residues play key roles in interaction with TA in the BmTA receptor.