Roles of accessory subunits in α4β2*nicotinic receptors
Roles of accessory subunits in α4β2*nicotinic receptors
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DOI：
10.1124/mol.108.046789
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发表时间：
2008-07-01
影响因子：
3.6
通讯作者：
Lindstrom, Jon
中科院分区：
文献类型：
--
作者：
Kuryatov, Alexandre;Onksen, Jennifer;Lindstrom, Jon
异聚体烟碱受体（AChRs）的辅助亚基不参与ACh结合位点的形成。α 5和β 3亚基只能起辅助亚基的作用。我们表明，α 5和β 3有效地组装在人类α 4 β 2* 乙酰胆碱受体表达在永久转染的人胚肾（HEK）细胞系。在脑中仅检测到（α 4 β 2）（2）α 5，而未检测到（α 4 β 2）（2）β 3 AChR。α 4 β 2 α 5系表达的AChR比亲本α 4 β 2* 系多40%，并且对尼古丁的上调同样敏感。α 4 β 2 β 3细胞系表达的乙酰胆碱受体比亲本细胞系多25倍，并且不能被尼古丁进一步上调。对乙酰胆碱激活的相对敏感性取决于辅助亚基，β 2赋予最大的敏感性，α 5较小，β 3和α 4小得多。辅助亚基形成正变构调节剂的结合位点，如观察到α 5赋予加兰他敏高敏感性所示。在α 5或β 3的存在下，稳定的、部分降解的、死端的中间体在细胞内积累。这些可以具有α 5 α 4 β 2 α 5的形式。α 5和β 3与α 4和β 2组装的效率以及避免形成潜在毒性中间体的必要性可以解释为什么α 5和β 3似乎在大脑中以低水平转录。常染色体显性夜间额叶癫痫可由α 4突变S247F引起。该突变体不产生功能性AChRs，除非细胞与α 5、β 3或α 6共转染以取代α 4作为辅助亚基。
Accessory subunits in heteromeric nicotinic receptors (AChRs) do not take part in forming ACh binding sites. alpha 5 and beta 3 subunits can function only as accessory subunits. We show that both alpha 5 and beta 3 efficiently assemble in human alpha 4 beta 2* AChRs expressed in permanently transfected human embryonic kidney (HEK) cell lines. Only (alpha 4 beta 2)(2)alpha 5, not (alpha 4 beta 2)(2)beta 3 AChRs, have been detected in brain. The alpha 4 beta 2 alpha 5 line expressed 40% more AChRs than the parent alpha 4 beta 2* line and was equally sensitive to up-regulation by nicotine. The alpha 4 beta 2 beta 3 line expressed 25-fold more AChRs than the parental line and could not be further up-regulated by nicotine. Relative sensitivity to activation by ACh depends on the accessory subunit, beta 2 conferring the greatest sensitivity, alpha 5 less, and beta 3 and alpha 4 much less. Accessory subunits form binding sites for positive allosteric modulators, as illustrated by the observation that alpha 5 conferred high sensitivity to galanthamine. In the presence of alpha 5 or beta 3, stable, partially degraded, dead end intermediates accumulated within the cells. These may have the form alpha 5 alpha 4 beta 2 alpha 5. The efficiency with which alpha 5 and beta 3 assemble with alpha 4 and beta 2 and the necessity of avoiding formation of potentially toxic intermediates may explain why alpha 5 and beta 3 seem to be transcribed at low levels in brain. Autosomal dominant nocturnal frontal lobe epilepsy can be caused by the alpha 4 mutation S247F. This mutant did not produce functional AChRs unless cells were cotransfected with alpha 5, beta 3, or alpha 6 to replace alpha 4 as accessory subunit.