Miner V W, Prestegard J H
Biochim Biophys Acta. 1984 Jul 25;774(2):227-36. doi: 10.1016/0005-2736(84)90296-7.
A comparative study of the structure of various phosphatidic acid-divalent cation complexes has been completed using 31P solids NMR methods. These complexes had been implicated as important intermediates in the fusion of phospholipid vesicles and several pieces of evidence had suggested that differences in activity of various ions may stem from structural differences among the complexes. Solids NMR studies using spin one-half nuclei reflect structural properties of molecules through partial averaging of chemical shift tensors. We have found significant differences in the chemical shift tensors observed for Mg, Ca and Cd complexes. Low angle X-ray scattering data were used to assure comparison of similar phases. At low temperatures Ca and Cd complexes exhibit unique phases prohibiting comparison with Mg complexes. At higher temperatures, all complexes exhibit a hexagonal phase, and 31P tensors of the complexes in the hexagonal phase can be interpreted using headgroup geometries similar to those found in crystal structures of phospholipids and assuming motional averaging by simple axial motions. Tensors of Ca and Cd complexes are very similar to one another but are significantly broader than those observed for Mg complexes suggesting a more erect headgroup structure. The differences parallel the fusion activities of the ions for which Ca and Cd are similar and significantly enhanced over that of Mg, supporting a structural link to fusion activity.
利用31P固体核磁共振方法完成了对各种磷脂酸 - 二价阳离子复合物结构的比较研究。这些复合物被认为是磷脂囊泡融合过程中的重要中间体，并且有几条证据表明，各种离子活性的差异可能源于复合物之间的结构差异。使用自旋1/2核的固体核磁共振研究通过化学位移张量的部分平均来反映分子的结构性质。我们发现，在Mg、Ca和Cd复合物中观察到的化学位移张量存在显著差异。利用低角度X射线散射数据来确保对相似相进行比较。在低温下，Ca和Cd复合物呈现出独特的相，无法与Mg复合物进行比较。在较高温度下，所有复合物都呈现出六方相，并且六方相中复合物的31P张量可以使用与磷脂晶体结构中发现的类似的头基几何形状，并假设通过简单的轴向运动进行运动平均来进行解释。Ca和Cd复合物的张量彼此非常相似，但明显比Mg复合物观察到的张量更宽，这表明头基结构更加直立。这些差异与离子的融合活性平行，其中Ca和Cd相似，并且比Mg的融合活性显著增强，这支持了与融合活性的结构联系。
