Gap junction structures. IV. Asymmetric features revealed by low-irradiation microscopy.
Gap junction structures. IV. Asymmetric features revealed by low-irradiation microscopy.
复制标题
间隙连接结构。
DOI：
10.1083/jcb.96.1.204
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
Goodenough,DA
中科院分区：
文献类型：
--
作者：
Baker,TS;Caspar,DL;Hollingshead,CJ;Goodenough,DA
小鼠肝脏缝隙连接的显微照片，分离与洗涤剂，负染色与醋酸铀酰，已被记录的低辐射的方法。我们的傅立叶平均显微照片的六边形连接晶格显示歪斜，六聚体连接与较少的染色在三倍轴比在六个缺口之间的叶的连接子图像。这些亚结构特征，以前没有清楚地观察到，是急性敏感的辐射。在电子剂量低于显微镜通常使用的剂量后，图像被转换为熟悉的甜甜圈形状，具有深色染色的中心和光滑的六边形轮廓，在晶格中具有镜像对称性。从我们的低辐射显微照片中重建的25个图像之间的外观差异说明了连接子通道和连接子之间的空间的染色的变化。在距离连接子中心约34 A的6个对称相关位点处一致观察到的染色浓度，与（1，1）晶格矢量的右侧或左侧成8度，可能揭示了连接结构的固有不对称特征。六叶连接子图像的意外偏斜表明，形成连接的一对六边形膜阵列在结构上可能不相同。由于连接子对本身的投影图像呈现镜像对称，因此每对连接子可能由两个相同的连接子六聚体组成，这些连接子六聚体通过差距中间的接合平面中的局部（非结晶学）双重轴相关。所有的连接子在化学上可能是相同的，但它们在连接点两侧的六边形阵列中的堆积似乎是不等价的。
Micrographs of mouse liver gap junctions, isolated with detergents, and negatively stained with uranyl acetate, have been recorded by low-irradiation methods. Our Fourier-averaged micrographs of the hexagonal junction lattice show skewed, hexameric connexons with less stain at the threefold axis than at the six indentations between the lobes of the connexon image. These substructural features, not clearly observed previously, are acutely sensitive to irradiation. After an electron dose less than that normally used in microscopy, the image is converted to the familiar doughnut shape, with a darkly stained center and a smooth hexagonal outline, oriented with mirror symmetry in the lattice. Differences in appearance among 25 reconstructed images from our low-irradiation micrographs illustrate variation in staining of the connexon channel and the space between connexons. Consistently observed stain concentration at six symmetrically related sites approximately 34 A from the connexon center, 8 degrees to the right or left of the (1, 1) lattice vector may reveal an intrinsic asymmetric feature of the junction structure. The unexpected skewing of the six-lobed connexon image suggests that the pair of hexagonal membrane arrays that form the junction may not be structurally identical. Because the projected image of the connexon pair itself appears mirror symmetric, each pair may consist of two identical connexon hexamers related by local (noncrystallographic) twofold axes in the junctional plane at the middle of the gap. All connexons may be chemically identical, but their packing in the hexagonal arrays on the two sides of the junction appears to be nonequivalent.