Kooijman Edgar E, Chupin Vladimir, de Kruijff Ben, Burger Koert N J
Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, the Netherlands.
Traffic. 2003 Mar;4(3):162-74. doi: 10.1034/j.1600-0854.2003.00086.x.
The local generation of phosphatidic acid plays a key role in the regulation of intracellular membrane transport through mechanisms which are largely unknown. Phosphatidic acid may recruit and activate downstream effectors, or change the biophysical properties of the membrane and directly induce membrane bending and/or destabilization. To evaluate these possibilities, we determined the phase properties of phosphatidic acid and lysophosphatidic acid at physiological conditions of pH and ion concentrations. In single-lipid systems, unsaturated phosphatidic acid behaved as a cylindrical, bilayer-preferring lipid at cytosolic conditions (37 degrees C, pH 7.2, 0.5 mM free Mg2+), but acquired a type-II shape at typical intra-Golgi conditions, a mildly acidic pH and submillimolar free Ca2+ (pH 6.6-5.9, 0.3 mM Ca2+). Lysophosphatidic acid formed type-I lipid micelles in the absence of divalent cations, but anhydrous cation-lysophosphatidic acid bilayer complexes in their presence. These data suggest a similar molecular shape for phosphatidic acid and lysophosphatidic acid at cytosolic conditions; however, experiments in mixed-lipid systems indicate that their shape is not identical. Lysophosphatidic acid stabilized the bilayer phase of unsaturated phosphatidylethanolamine, while the opposite effect was observed in the presence of phosphatidic acid. These results support the hypothesis that a conversion of lysophosphatidic acid into phosphatidic acid by endophilin or BARS (50 kDa brefeldin A ribosylated substrate) may induce negative spontaneous monolayer curvature and regulate endocytic and Golgi membrane fission. Alternative models for the regulation of membrane fission based on the strong dependence of the molecular shape of (lyso)phosphatidic acid on pH and divalent cations are also discussed.
磷脂酸的局部生成在细胞内膜运输调节中起着关键作用，但其机制大多未知。磷脂酸可能招募并激活下游效应器，或改变膜的生物物理性质，直接诱导膜弯曲和/或不稳定。为评估这些可能性，我们测定了在生理pH和离子浓度条件下磷脂酸和溶血磷脂酸的相性质。在单脂质体系中，不饱和磷脂酸在胞质条件下（37℃，pH 7.2，0.5 mM游离Mg2+）表现为柱状、偏好双层的脂质，但在典型的高尔基体内部条件下，即在轻度酸性pH和亚毫摩尔游离Ca2+（pH 6.6 - 5.9，0.3 mM Ca2+）时呈现II型形状。溶血磷脂酸在没有二价阳离子的情况下形成I型脂质微团，但在有二价阳离子存在时形成无水阳离子 - 溶血磷脂酸双层复合物。这些数据表明在胞质条件下磷脂酸和溶血磷脂酸具有相似的分子形状；然而，混合脂质体系中的实验表明它们的形状并不相同。溶血磷脂酸稳定了不饱和磷脂酰乙醇胺的双层相，而在磷脂酸存在时则观察到相反的效果。这些结果支持这样的假说，即内吞蛋白或BARS（50 kDa布雷菲德菌素A核糖基化底物）将溶血磷脂酸转化为磷脂酸可能诱导负的自发单层曲率，并调节内吞和高尔基体膜裂变。还讨论了基于（溶血）磷脂酸分子形状对pH和二价阳离子的强烈依赖性的膜裂变调节的替代模型。
