Arrondo J L, Mantsch H H, Mullner N, Pikula S, Martonosi A
J Biol Chem. 1987 Jul 5;262(19):9037-43.
The Ca2+-transporting ATPase (EC 3.6.1.38) of sarcoplasmic reticulum alternates between several conformational states during ATP-dependent Ca2+ transport. The E1 conformation is stabilized by 0.1 mM Ca2+ and the E2 conformation by vanadate in a Ca2+-free medium. Fourier transform infrared spectroscopy reveals significant differences between the two states that indicate differences in the protein secondary structure. The two states and the corresponding spectra can be interconverted reversibly by changing the Ca2+ concentration of the medium. The infrared spectral changes indicate the appearance of a new alpha-helical substructure connected with the E1----E2 conversion accompanied by small changes in beta-turns, while the beta-sheet content remains essentially unchanged. There are also differences between the E1 and E2 states in the C = O stretching vibrations of the ester carbonyl groups of phospholipids in intact sarcoplasmic reticulum that are not observed under identical conditions in isolated sarcoplasmic reticulum lipid dispersions. These observations imply an effect of proteins on the structure of the interfacial regions of the phospholipids that is dependent on the conformational state of the Ca2+-ATPase. The CH2- and CH3-stretching frequencies of the membrane lipids are not affected significantly by the E1----E2 transition. The Fourier transform infrared spectra of sarcoplasmic reticulum vesicles in the presence of 20 mM Ca2+ suggest the stabilization of a protein conformation similar to the E2 state except for differences in the behavior of COO- and phospholipid ester C = O groups that may reflect charge effects of the bound Ca2+.
肌质网的Ca2+转运ATP酶（EC 3.6.1.38）在ATP依赖的Ca2+转运过程中会在几种构象状态之间交替。在0.1 mM Ca2+存在下E1构象得以稳定，而在无Ca2+的介质中钒酸盐可稳定E2构象。傅里叶变换红外光谱揭示了这两种状态之间存在显著差异，表明蛋白质二级结构存在差异。通过改变介质的Ca2+浓度，这两种状态及相应光谱可进行可逆的相互转换。红外光谱变化表明出现了一种与E1→E2转换相关的新的α螺旋亚结构，同时β转角有微小变化，而β折叠含量基本保持不变。完整肌质网中磷脂酯羰基的C=O伸缩振动在E1和E2状态之间也存在差异，而在相同条件下分离的肌质网脂质分散体中未观察到这种差异。这些观察结果表明蛋白质对磷脂界面区域结构有影响，这种影响取决于Ca2+-ATP酶的构象状态。膜脂质的CH2和CH3伸缩频率不受E1→E2转变的显著影响。在20 mM Ca2+存在下肌质网小泡的傅里叶变换红外光谱表明，除了COO-和磷脂酯C=O基团行为的差异可能反映结合Ca2+的电荷效应外，一种类似于E2状态的蛋白质构象得以稳定。
