Transmembrane domains (TMDs) I, II, and VII of the β2-adrenergic receptor (β2AR) were replaced, individually or in combination, with the corresponding regions of the β1AR, and vice versa. The β2-selective binding of salmeterol was not affected by the exchange of TMD I between the β1- and β2ARs. The affinity of salmeterol was slightly decreased (32- fold) by replacement of TMD II of the β2AR with the homologous region of the β1AR; the affinity was strongly decreased (1870-fold) for the β2AR with TMD VII of the β1AR. The affinity of salmeterol was partially restored by the introduction of TMD VII, but not TMD II, of the β2AR into the β1AR. By analyzing alanine-substituted mutants, we found that Tyr308 in TMD VII was mainly responsible for the high affinity binding of salmeterol. Two salmeterol derivatives with the ether oxygen at different positions in the side chain showed 33- and 64-fold decreased affinities for the wild-type β2AR, and a derivative with no ether oxygen showed 147-fold decreased affinity for the wild-type β2AR. These results indicate that Tyr308 in TMD VII is the major amino acid conferring the β2-selective binding of salmeterol to the β2AR and that the position of the ether oxygen in the side chain is also important for β2-selective binding. A three-dimensional model of the salmeterol-β2AR complex shows that the phenyl group of Tyr308 interacts with methylene groups near the protonated amine of salmeterol and the ether oxygen interacts with Tyr316.
|出版ステータス||出版済み - 10月 1998|
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