Forsayeth J R, Kobrin E
Department of Anesthesia, University of California San Francisco, San Francisco, California 94143-0542, USA.
J Neurosci. 1997 Mar 1;17(5):1531-8. doi: 10.1523/JNEUROSCI.17-05-01531.1997.
The role of the beta3 and beta4 subunits of the nicotinic acetylcholine receptor in brain is still unclear. We investigated nicotinic receptor structure with antibodies directed against unique regions of the beta3 and beta4 subunits of the rat nicotinic acetylcholine receptor. Anti-beta4 detected a single band of 66 kDa in most regions of the brain that was strongest in striatum and cerebellum. The 60 kDa beta3 subunit was detected primarily in striatum and cerebellum, and faintly in hippocampus. Immunoprecipitation experiments established that the two subunits were coassembled in the cerebellum along with the beta2 subunit. Antibodies against the alpha4, beta2, beta3, and beta4 subunits immunoprecipitated approximately 75% of the bungarotoxin-insensitive nicotinic receptor from cerebellar extracts as determined by nicotine-dependent acetylcholine binding. Transfection of COS cells with cDNAs for these four subunits induced expression of a high affinity nicotinic receptor. Omission of only a single subunit from the transfection affected either the Bmax or the apparent KD of the receptor. Our data suggest that the beta3 subunit functions as a structural entity that links a relatively unstable alpha4beta2 heterodimer to a more stable alpha4beta4 heterodimer. The agonist-binding site formed by alpha4beta2 has a much greater affinity than does that formed by alpha4beta4. In this respect, nicotinic receptors that contain the beta3 subunit are structurally homologous to the muscle nicotinic receptor.
烟碱型乙酰胆碱受体的β3和β4亚基在大脑中的作用仍不清楚。我们用针对大鼠烟碱型乙酰胆碱受体β3和β4亚基独特区域的抗体研究了烟碱型受体结构。抗β4抗体在大脑的大多数区域检测到一条66 kDa的单带，在纹状体和小脑中最强。60 kDa的β3亚基主要在纹状体和小脑中检测到，在海马体中较弱。免疫沉淀实验表明，这两个亚基与β2亚基一起在小脑中共同组装。通过尼古丁依赖性乙酰胆碱结合测定，针对α4、β2、β3和β4亚基的抗体从脑提取物中免疫沉淀了约75%的不敏感于银环蛇毒素的烟碱型受体。用这四个亚基的cDNA转染COS细胞诱导了高亲和力烟碱型受体的表达。转染时仅缺失一个亚基就会影响受体的Bmax或表观KD。我们的数据表明，β3亚基作为一个结构实体，将相对不稳定的α4β2异二聚体与更稳定的α4β4异二聚体联系起来。由α4β2形成的激动剂结合位点比由α4β4形成的具有更高的亲和力。在这方面，含有β3亚基的烟碱型受体在结构上与肌肉烟碱型受体同源。
