GABABRs are key membrane proteins that continually adapt the excitability of the nervous system. These G-protein coupled receptors are activated by the brain’s premier inhibitory neurotransmitter GABA. They are obligate heterodimers composed of GABA-binding GABABR1 and G-protein-coupling GABABR2 subunits. Recently, three variants (G693W, S695I, I705N) have been identified in the gene (GABBR2) encoding for GABABR2. Individuals that harbour any of these variants exhibit severe developmental epileptic encephalopathy and intellectual disability, but the underlying pathogenesis that is triggered in neurons, remains unresolved. Using a range of confocal imaging, flow cytometry, structural modelling, biochemistry, live cell Ca2+ imaging of presynaptic terminals, whole-cell electrophysiology of HEK-293T cells and neurons, and two-electrode voltage clamping of Xenopus oocytes we have probed the biophysical and molecular trafficking and functional profiles of G693W, S695I and I705N variants. We report that all three point mutations impair neuronal cell surface expression of GABABRs, reducing signalling efficacy. However, a negative effect evident for one variant perturbed neurotransmission by elevating presynaptic Ca2+ signalling. This is reversed by enhancing GABABR signalling via positive allosteric modulation. Our results highlight the importance of studying neuronal receptors expressed in nervous system tissue and provide new mechanistic insights into how GABABR variants can initiate neurodevelopmental disease whilst highlighting the translational suitability and therapeutic potential of allosteric modulation for correcting these deficits.

中文翻译：

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GABABR 癫痫变异体的正向变构调节可逆转突触前过度兴奋


GABABR 是持续调节神经系统兴奋性的关键膜蛋白。这些 G 蛋白偶联受体由大脑主要的抑制性神经递质 GABA 激活。它们是由 GABA 结合 GABABR1 和 G 蛋白偶联 GABABR2 亚基组成的专性异二聚体。最近，在编码 GABABR2 的基因 (GABBR2) 中发现了三个变体 (G693W、S695I、I705N)。携带任何这些变异的个体表现出严重的发育性癫痫性脑病和智力障碍，但在神经元中触发的潜在发病机制仍未解决。使用一系列共聚焦成像、流式细胞术、结构建模、生物化学、突触前末梢的活细胞 Ca2+ 成像、HEK-293T 细胞和神经元的全细胞电生理学以及非洲爪蟾卵母细胞的双电极电压钳，我们已经探讨了生物物理和G693W、S695I 和 I705N 变体的分子运输和功能概况。我们报告，所有三个点突变都会损害 GABABR 的神经元细胞表面表达，从而降低信号传导功效。然而，一种变体通过提高突触前 Ca2+ 信号传导而扰乱神经传递，从而产生明显的负面影响。通过正变构调节增强 GABABR 信号传导可以逆转这一情况。我们的结果强调了研究神经系统组织中表达的神经元受体的重要性，并为 GABABR 变体如何引发神经发育疾病提供了新的机制见解，同时强调了变构调节纠正这些缺陷的转化适用性和治疗潜力。