PDF(Pubmed)
Abstract：
BK K+ channels are critical regulators of neuron and muscle excitability, comprised of a tetramer of pore-forming αsubunits from the KCNMA1 gene and cell- and tissue-selective β subunits (KCNMB1-4). Mutations in KCNMA1 are associated with neurological disorders, including autism. However, little is known about the role of neuronal BK channel β subunits in human neuropathology. The β2 subunit is expressed in central neurons and imparts inactivation to BK channels, as well as altering activation and deactivation gating. In this study, we report the functional effect of G124R, a novel KCNMB2 mutation obtained from whole-exome sequencing of a patient diagnosed with autism spectrum disorder. Residue G124, located in the extracellular loop between TM1 and TM2, is conserved across species, and the G124R missense mutation is predicted deleterious with computational tools. To investigate the pathogenicity potential, BK channels were co-expressed with β2WT and β2G124R subunits in HEK293T cells. BK/β2 currents were assessed from inside-out patches under physiological K+ conditions (140/6 mM K+ and 10 μM Ca2+) during activation and inactivation (voltage-dependence and kinetics). Using β2 subunits lacking inactivation (β2IR) revealed that currents from BK/β2IRG124R channels activated 2-fold faster and deactivated 2-fold slower compared with currents from BK/β2IRWT channels, with no change in the voltage-dependence of activation (V1/2). Despite the changes in the BK channel opening and closing, BK/β2G124R inactivation rates (τinact and τrecovery), and the V1/2 of inactivation, were unaltered compared with BK/β2WT channels under standard steady-state voltage protocols. Action potential-evoked current was also unchanged. Thus, the mutant phenotype suggests the β2G124R TM1-TM2 extracellular loop could regulate BK channel activation and deactivation kinetics. However, additional evidence is needed to validate pathogenicity for this patient-associated variant in KCNMB2.
摘要：
BKK+通道是神经元和肌肉兴奋性的关键调节因子，由来自KCNMA1基因的成孔α亚基和细胞和组织选择性β亚基（KCNMB1-4）的四聚体组成。KCNMA1的突变与神经系统疾病有关，包括自闭症。然而,关于神经元BK通道β亚基在人类神经病理学中的作用知之甚少。β2亚基在中枢神经元中表达，并使BK通道失活，以及改变激活和去激活门控。在这项研究中,我们报道了G124R的功能效应，从1例自闭症谱系障碍患者的全外显子组测序中获得的一种新的KCNMB2突变.残基G124位于TM1和TM2之间的胞外环中，在物种之间是保守的，G124R错义突变是用计算工具预测的。为了研究致病性潜力，BK通道在HEK293T细胞中与β2WT和β2G124R亚基共表达。在激活和失活过程中（电压依赖性和动力学），在生理K条件（140/6mMK和10μMCa2）下，从内向外的贴片评估BK/β2电流。使用缺乏失活的β2亚基（β2IR）表明，与来自BK/β2IRWT通道的电流相比，来自BK/β2IRG124R通道的电流激活快2倍，失活慢2倍，激活的电压依赖性没有变化（V1/2）。尽管BK通道的打开和关闭发生了变化，BK/β2G124R失活率（τinact和τrecovery），和失活的V1/2，在标准稳态电压方案下，与BK/β2WT通道相比没有改变。动作电位诱发的电流也没有变化。因此，突变表型表明β2G124RTM1-TM2胞外环可以调节BK通道的激活和失活动力学。然而,需要更多的证据来验证KCNMB2中这种患者相关变异体的致病性.
