Taylor K A, Dux L, Martonosi A
J Mol Biol. 1986 Feb 5;187(3):417-27. doi: 10.1016/0022-2836(86)90442-0.
The structure of the Ca2+ transport ATPase from rabbit skeletal muscle sarcoplasmic reticulum has been determined to 25 A resolution by three-dimensional image reconstruction of crystalline membrane tubules induced through exposure to Na3VO4 and preserved for electron microscopy in negative stain. The crystalline arrays have projection symmetry p2 and consist of chains of Ca2+-ATPase dimers arranged in a right-handed helix. The density map shows protein features that project from the membrane surface into the cytoplasm. The luminal side of the membrane tubules is featureless, presumably because very little of the Ca2+-ATPase molecule projects into the luminal space. The cytoplasmic region of the Ca2+-ATPase molecule is pear-shaped, with a lobe oriented nearly parallel to the axis of the dimer ribbons, about 16 A above the surface of the membrane bilayer. The structure seen in the maps has a volume of 71,000 A3, corresponding to a molecular weight of 57,000. The two Ca2+-ATPase profiles that constitute a dimer are connected by a stain-excluding bridge that is oriented parallel with the axis of the tubule at a height of about 42 A above the surface of the bilayer.
通过对经 Na3VO4 诱导形成并在负染下保存用于电子显微镜观察的晶体膜小管进行三维图像重建，已确定兔骨骼肌肌浆网中 Ca2+ 转运 ATP 酶的结构分辨率达到 25 Å。晶体阵列具有 p2 投影对称性，由排列成右手螺旋的 Ca2+ -ATP 酶二聚体链组成。密度图显示了从膜表面伸向细胞质的蛋白质特征。膜小管的腔面没有特征，推测是因为 Ca2+ -ATP 酶分子很少伸向腔隙空间。Ca2+ -ATP 酶分子的细胞质区域呈梨形，有一个叶几乎平行于二聚体带的轴，位于膜双层表面上方约 16 Å 处。图中看到的结构体积为 71,000 Å3，对应分子量为 57,000。构成二聚体的两个 Ca2+ -ATP 酶轮廓通过一个排染桥相连，该桥在双层表面上方约 42 Å 处平行于小管轴定向。
