Four amino acids in the α subunits determine the γ-aminobutyric acid sensitivities of GABAA receptor subtypes
Four amino acids in the α subunits determine the γ-aminobutyric acid sensitivities of GABAA receptor subtypes
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DOI：
10.1074/jbc.m405653200
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发表时间：
2004-08-20
影响因子：
4.8
通讯作者：
Lüddens, H
中科院分区：
文献类型：
--
作者：
Böhme, I;Rabe, H;Lüddens, H
GABA(A) 受体是快速抑制性神经传递的介质，是由大量亚基组成的异五聚体。受体亚型对内源性 GABA 的敏感性差异可能允许对相同 GABA 能输入的亚基依赖性微调响应。利用放射性配体结合和电生理学与诱变相结合，我们鉴定了α亚基内的四个氨基酸结构域，该结构域介导对GABA的不同敏感性，从而允许它们在alpha3gamma2组合之间选择性切换。用 alpha1-alpha5 的相应片段替换 alpha3 中的该结构域导致突变受体显示各自野生型受体的 GABA EC50 值。反之亦然，alpha3 基序迫使 alpha1beta3gamma2、alpha4beta3gamma2 和 alpha5beta3gamma2 的 alpha3 对 GABA 的敏感性较低。 GABA 激动剂 [H-3] 蝇蕈醇的结合不受 α1 和 α3 亚基之间基序交换的影响。因此，在替换四个氨基酸后平衡结合袋得以维持。总的来说，我们的数据表明，所识别的基序有助于参与结合信号转导的结构，而不是结合本身。
GABA(A) receptors, mediators of fast inhibitory neurotransmission, are heteropentameric assemblies from a large array of subunits. Differences in the sensitivity of receptor subtypes to endogenous GABA may permit subunit-dependent finely tuned responsiveness to the same GABAergic inputs. Using both radioligand binding and electrophysiology combined with mutagenesis, we identified a domain of four amino acids within the alpha subunits that mediates the distinct sensitivities to GABA allowing their selective switch between alphabeta3gamma2 combinations. Replacing this domain in alpha3 by the corresponding segments of alpha1-alpha5 resulted in mutant receptors displaying the GABA EC50 values of the respective wild-type receptors. Vice versa, the alpha3 motif forced the low sensitivity to GABA of alpha3 upon alpha1beta3gamma2, alpha4beta3gamma2, and alpha5beta3gamma2. Binding of the GABA agonist [H-3] muscimol was not affected by the exchange of the motif between alpha1 and alpha3 subunits. Thus, the equilibrium binding pocket is maintained upon replacement of the four amino acids. Taken together our data suggest that the identified motifs contribute to a structure involved in the transduction of the binding signal rather than to the binding itself.