Physical properties of the transmembrane signal molecule, sn-1-stearoyl 2-arachidonoylglycerol -: Acyl chain segregation and its biochemical implications
Physical properties of the transmembrane signal molecule, sn-1-stearoyl 2-arachidonoylglycerol -: Acyl chain segregation and its biochemical implications
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DOI：
10.1074/jbc.275.10.6857
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发表时间：
2000-03-10
影响因子：
4.8
通讯作者：
Holmsen, H
中科院分区：
文献类型：
--
作者：
Hindenes, JO;Nerdal, W;Holmsen, H
sn-1，2-二酰基甘油（DAG）是脂质代谢中的关键中间体，其激活蛋白激酶C并且是融合剂。磷酸肌醇是细胞信号传导中DAG的主要来源，主要分别在sn-1和sn-2位含有硬脂酰基和花生四烯酸酰基。用差示扫描量热法、X射线粉末衍射法和固体魔角旋转（MAS）C-13 NMR研究了sn-1-硬脂酰-2-花生四烯酸酰甘油（SAG）的多晶型行为。X射线衍射分析表明，酰基链在α相中呈六方排列，两个亚α相呈假六方对称排列。在窄角度范围内，存在类似于31埃和类似于62埃的强衍射。各向同性SAG的高功率质子解耦MAS C-13 NMR给出了20个花生四烯酸碳的16个不同的共振和18个硬脂酰碳的5个不同的共振。在冷却时，硬脂酰基的所有共振在亚α相中减弱并消失，而花生四烯酰基碳从8/6到20在冷冻相中给出不同的共振。值得注意的是，两个酰基链的ω-碳在α、亚α（1）和亚α（2）相中具有不同的化学位移。通过固相α、亚α（1）和亚α（2）中的接触时间（交叉极化）MAS C-13 NMR实验，证明了硬脂酰基和花生四烯酰基亚甲基和甲基的自旋晶格弛豫的巨大差异。这表明SAG中的硬脂酰基和花生四烯酸酰基在固态（α、亚α（1）和亚α（2）相）中具有不同的环境，并且在冷却期间可能分离。NMR和长间距X-射线衍射结果表明，SAG不包装在一个传统的双层与两个酰基在发夹的方式。因此，我们的研究结果提供了一个物理化学基础的DAG六角相域分离膜双层。
sn-1,2-Diacylglycerol (DAG), a key intermediate in lipid metabolism activates protein kinase C and is a fusogen. Phosphoinositides, the main sources of DAG in cell signaling, contain mostly stearoyl and arachidonoyl in the sn-1 and -2 positions, respectively. The polymorphic behavior of sn-1-stearoyl-2-arachidonoylglycerol (SAG) was studied by differential scanning calorimetry, x-ray powder diffraction, and solid state magic angle spinning (MAS) C-13 NMR, Three alpha phases were found in the dry state. X-ray diffraction indicated that the acyl chains packed in a hexagonal array in the alpha phase, and the two sub-alpha phases packed with pseudo-hexagonal symmetry. In the narrow angle range strong diffractions of similar to 31 and similar to 62 Angstrom were present. High power proton-decoupled MAS C-13 NMR of isotropic SAG gave 16 distinct resonances of the 20 arachidonoyl carbons and 5 distinct resonances of the 18 stearoyl carbons. Upon cooling, all resonances of stearoyl weakened and vanished in the sub-alpha, phase, whereas arachidonoyl carbons from 8/6 to 20 gave distinct resonances in the frozen phases. Remarkably, the omega-carbon of the two acyl chains had different chemical shifts in alpha, sub-alpha(1), and sub-alpha(2) phases. Large differences in spin lattice relaxation of the stearoyl and arachidonoyl methene and methyl groups were demonstrated by contact time (cross-polarization) MAS C-13 NMR experiments in the solid phases alpha, sub-alpha(1), and sub-alpha(2). This shows that stearoyl and arachidonoyl in SAG have different environments in the solid states (alpha, sub-alpha(1), and sub-alpha(2) phases) and may segregate during cooling. The NMR and long spacing x-ray diffraction results suggest that SAG does not pack in a conventional double layer with the two acyls in a hairpin fashion. Our findings thus provide a physicochemical basis for DAG hexagonal phase domain separation within membrane bilayers.