Lal R, Yu L
Department of Medicine, University of Chicago, IL 60637.
Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7280-4. doi: 10.1073/pnas.90.15.7280.
The nicotinic acetylcholine receptor (AChR) was expressed in Xenopus oocytes from in vitro transcribed mRNA and was imaged by atomic force microscopy. A characteristic pentameric structure of AChR was readily observed on the extracellular face of the cell membrane, with a central pore surrounded by protruding AChR subunits. These structures were seen only in mRNA-injected oocytes that also gave acetylcholine-induced membrane currents. The size of individual AChR channels, the angles between subunits, and the interchannel spacing were all compatible with the current model of AChR. In addition, localized patches of microscopic AChR clustering were observed, with packing density approaching that at the neuromuscular junction. These findings show the potential of studying cloned membrane proteins in oocytes for both their surface topography and their structure-function relationship in native membrane without the need for crystallization.
烟碱型乙酰胆碱受体（AChR）通过体外转录的mRNA在非洲爪蟾卵母细胞中表达，并通过原子力显微镜成像。在细胞膜的细胞外表面很容易观察到AChR典型的五聚体结构，中央孔被突出的AChR亚基包围。这些结构仅在注射了mRNA且也产生乙酰胆碱诱导的膜电流的卵母细胞中可见。单个AChR通道的大小、亚基之间的角度以及通道间间距均与当前的AChR模型相符。此外，还观察到微观AChR聚集的局部斑块，其堆积密度接近神经肌肉接头处的密度。这些发现表明，在卵母细胞中研究克隆的膜蛋白，对于其表面形貌以及在天然膜中的结构-功能关系而言，具有无需结晶即可进行研究的潜力。
