Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Orgánica, Buenos Aires, Argentina; CONICET - Universidad de Buenos Aires, UMYMFOR, Buenos Aires, Argentina.
Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Buenos Aires, Argentina; CONICET - Universidad de Buenos Aires, IFIBYNE, Buenos Aires, Argentina.
J Steroid Biochem Mol Biol. 2018 Sep;182:72-80. doi: 10.1016/j.jsbmb.2018.04.012. Epub 2018 Apr 26.
Neurosteroids are the principal endogenous modulators of the γ-Aminobutyric acid receptors (GABARs), pentameric membrane-bound proteins that can be assembled from at least 19 subunits. In the most abundant GABAR arrangement (αβγ), neurosteroids can potentiate the GABA action as well as produce a direct activation of the channel. The recent crystal structures of neurosteroids bound to α homopentameric GABAR reveal binding to five equivalent sites. However, these results have been obtained using receptors that are not physiologically relevant, suggesting a need to investigate neurosteroid binding to heteropentameric receptors that exist in the central nervous system. In a previous work, we predicted the neurosteroid binding site by applying molecular modeling methods on the β homopentamer. Here we construct a homology model of the transmembrane domain of the heteropentameric αβγ receptor and then, by combining docking and molecular dynamics simulations, we analyzed neurosteroid binding. Results show that the five neurosteroid cavities are conserved in the αβγ receptor and all of them are able to bind neurosteroids. Two different binding modes were detected depending on the identity of the residue at position 241 in the transmembrane helix 1. These theoretical findings provide microscopic insights into neurosteroid binding at the heteropentameric GABAR. The existence of two classes of sites may be associated with how neurosteroids modulate GABAR. Our finding would represent the essential first step to reach a comprehensive understanding of how these endogenous molecules regulate the central nervous system.
神经甾体是 γ-氨基丁酸受体（GABAR）的主要内源性调节剂，GABAR 是一种五聚体膜结合蛋白，可由至少 19 个亚基组成。在最丰富的 GABAR 排列（αβγ）中，神经甾体可以增强 GABA 的作用，并直接激活通道。最近，与α同源五聚体 GABAR 结合的神经甾体的晶体结构揭示了与五个等效结合位点的结合。然而，这些结果是使用与生理无关的受体获得的，这表明有必要研究神经甾体与存在于中枢神经系统中的异源五聚体受体的结合。在之前的工作中，我们通过对β同源五聚体应用分子建模方法来预测神经甾体结合位点。在这里，我们构建了异源五聚体αβγ受体跨膜域的同源模型，然后通过结合对接和分子动力学模拟来分析神经甾体结合。结果表明，在αβγ受体中，五个神经甾体腔是保守的，并且它们都能够结合神经甾体。根据跨膜螺旋 1 中 241 位残基的身份，检测到两种不同的结合模式。这些理论发现为异源五聚体 GABAR 中的神经甾体结合提供了微观见解。两种结合位点的存在可能与神经甾体如何调节 GABAR 有关。我们的发现将代表达到全面理解这些内源性分子如何调节中枢神经系统的重要的第一步。
