Dux L, Taylor K A, Ting-Beall H P, Martonosi A
J Biol Chem. 1985 Sep 25;260(21):11730-43.
Two-dimensional crystalline arrays of Ca2+-ATPase molecules develop in sarcoplasmic reticulum vesicles exposed to Ca2+ or lanthanide ions. The Ca2+- or lanthanide-induced crystals are presumed to represent the E1 conformation of the Ca2+-ATPase, and their crystal form is clearly different from the earlier described E2 crystals induced by Na3VO4 in the presence of ethylene glycol bis(beta aminoethyl ether)-N,N,N',N'-tetraacetic acid (Taylor, K. A., Dux, L., and Martonosi, A. (1984) J. Mol. Biol. 174, 193-204). Analysis of the crystalline arrays by negative staining or freeze-fracture electron microscopy reveals obliquely oriented rows of particles corresponding to individual Ca2+-ATPase molecules. Computer analysis of the negatively stained lanthanide-induced crystalline Ca2+-ATPase arrays shows that the molecules are arranged in a P1 lattice. The pear-shaped profiles of Ca2+-ATPase molecules seen in projection in the density maps are similar to those seen in vanadate-induced crystals. The space group and unit cell dimensions of the E1 crystals are consistent with Ca2+-ATPase monomers as structural units, while the vanadate-induced E2 crystals form by lateral aggregation of chains of Ca2+-ATPase dimers. The transition between the E1 and E2 conformations may involve a shift in the monomer-oligomer equilibrium of the Ca2+-ATPase. The formation of E1 crystals by PrCl3 is promoted by inside negative membrane potential, presumably through stabilization of the E1 conformation of the enzyme. Cleavage of the Ca2+-ATPase by trypsin into two major fragments (A and B) did not interfere with the Ca2+- or the Pr3+-induced crystallization.
在暴露于钙离子或镧系离子的肌浆网小泡中会形成钙离子 - ATP酶分子的二维晶体阵列。钙离子或镧系离子诱导形成的晶体被认为代表了钙离子 - ATP酶的E1构象，并且它们的晶体形态与之前描述的在乙二醇双（β - 氨基乙基醚）- N，N，N'，N'-四乙酸存在下由偏钒酸钠诱导形成的E2晶体明显不同（泰勒，K. A.，达克斯，L.，和马托诺西，A.（1984年）《分子生物学杂志》174卷，193 - 204页）。通过负染色或冷冻断裂电子显微镜对晶体阵列进行分析，可揭示出对应于单个钙离子 - ATP酶分子的倾斜排列的颗粒行。对负染色的镧系离子诱导的晶体状钙离子 - ATP酶阵列进行计算机分析表明，分子排列在P1晶格中。在密度图投影中看到的钙离子 - ATP酶分子的梨形轮廓与在钒酸盐诱导的晶体中看到的相似。E1晶体的空间群和晶胞尺寸与作为结构单元的钙离子 - ATP酶单体一致，而钒酸盐诱导的E2晶体是由钙离子 - ATP酶二聚体链的侧向聚集形成的。E1和E2构象之间的转变可能涉及钙离子 - ATP酶单体 - 寡聚体平衡的变化。氯化镨促进E1晶体的形成，这可能是通过稳定酶的E1构象，借助膜内负电位实现的。用胰蛋白酶将钙离子 - ATP酶切割成两个主要片段（A和B）并不影响钙离子或镨离子诱导的结晶作用。
