Ehya Noosha, Sarto Isabella, Wabnegger Leila, Sieghart Werner
Division of Biochemistry and Molecular Biology, Brain Research Institute, University of Vienna, Austria.
J Neurochem. 2003 Jan;84(1):127-35. doi: 10.1046/j.1471-4159.2003.01509.x.
GABA(A) receptors are chloride ion channels that can be opened by GABA, the most important inhibitory transmitter in the CNS. In the mammalian brain the majority of these pentameric receptors is composed of two alpha, two beta and one gamma subunit. To achieve the correct order of subunits around the pore, each subunit must form specific contacts via its plus (+) and minus (-) side. To identify a sequence on the beta3 subunit important for assembly, we generated various full-length or truncated chimeric beta3 constructs and investigated their ability to assemble with alpha1 and gamma2 subunits. It was demonstrated that replacement of the sequence beta3(76-89) by the homologous alpha1 sequence impaired assembly with alpha1 but not with gamma2 subunits in alpha1beta3gamma2-GABA(A) receptors. Other experiments indicated that assembly was impaired via the beta3(-) side of the chimeric subunit. Within the sequence beta3(76-89) the sequence beta3(85-89) seemed to be of primary importance for assembly with alpha1 subunits. A comparison with the structure of the acetylcholine-binding protein supports the conclusion that the sequence beta3(85-89) is located at the beta3(-) side and indicates that it contains amino acid residues that might directly interact with the (+) side of the neighbouring alpha1 subunit.
GABA(A)受体是氯离子通道，可被γ-氨基丁酸（GABA，中枢神经系统中最重要的抑制性递质）打开。在哺乳动物大脑中，这些五聚体受体大多数由两个α亚基、两个β亚基和一个γ亚基组成。为了使亚基围绕孔道形成正确的排列顺序，每个亚基必须通过其正（+）侧和负（-）侧形成特定的接触。为了确定β3亚基上对组装重要的序列，我们构建了各种全长或截短的嵌合β3构建体，并研究了它们与α1和γ2亚基组装的能力。结果表明，在α1β3γ2 - GABA(A)受体中，用同源的α1序列替换β3(76 - 89)序列会损害与α1亚基的组装，但不会损害与γ2亚基的组装。其他实验表明，组装是通过嵌合亚基的β3（-）侧受损的。在β3(76 - 89)序列中，β3(85 - 89)序列似乎对与α1亚基的组装最为重要。与乙酰胆碱结合蛋白结构的比较支持了β3(85 - 89)序列位于β3（-）侧的结论，并表明它包含可能与相邻α1亚基的（+）侧直接相互作用的氨基酸残基。
