School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.
Mol Pharmacol. 2011 Apr;79(4):742-8. doi: 10.1124/mol.110.069583. Epub 2011 Jan 25.
Cation-π interactions have been demonstrated to play a major role in agonist-binding in Cys-loop receptors. However, neither the aromatic amino acid contributing to this interaction nor its location is conserved among Cys-loop receptors. Likewise, it is not clear how many different agonists of a given receptor form a cation-π interaction or, if they do, whether it is with the same aromatic amino acid as the major physiological agonist. We demonstrated previously that Phe159 in the glycine receptor (GlyR) α1 subunit forms a strong cation-π interaction with the principal agonist, glycine. In the current study, we investigated whether the lower efficacy agonists of the human GlyR β-alanine and taurine also form cation-π interactions with Phe159. By incorporating a series of unnatural amino acids, we found cation-π interactions between Phe159 and the amino groups of β-alanine and taurine. The strengths of these interactions were significantly weaker than for glycine. Modeling studies suggest that β-alanine and taurine are orientated subtly differently in the binding pocket, with their amino groups further from Phe159 than that of glycine. These data therefore show that similar agonists can have similar but not identical orientations and interactions in the binding pocket and provide a possible explanation for the lower potencies of β-alanine and taurine.
阳离子-π 相互作用已被证明在 Cys 环受体的激动剂结合中起主要作用。然而，在 Cys 环受体中，既没有参与这种相互作用的芳香族氨基酸，也没有其位置是保守的。同样，也不清楚给定受体的多少种不同激动剂形成阳离子-π 相互作用，或者如果它们确实形成了这种相互作用，是否与主要生理激动剂的芳香族氨基酸相同。我们之前已经证明，甘氨酸受体 (GlyR)α1 亚基中的苯丙氨酸 159 与主要激动剂甘氨酸形成强阳离子-π 相互作用。在当前的研究中，我们研究了人类 GlyRβ-丙氨酸和牛磺酸的低效能激动剂是否也与苯丙氨酸 159 形成阳离子-π 相互作用。通过掺入一系列非天然氨基酸，我们发现苯丙氨酸 159 与β-丙氨酸和牛磺酸的氨基之间存在阳离子-π 相互作用。这些相互作用的强度明显弱于甘氨酸。建模研究表明，β-丙氨酸和牛磺酸在结合口袋中的取向略有不同，其氨基离苯丙氨酸 159 比甘氨酸更远。这些数据表明，类似的激动剂可以在结合口袋中具有相似但不相同的取向和相互作用，并为β-丙氨酸和牛磺酸的低效力提供了可能的解释。
