We investigated the deformation of small unilamellar vesicles (SUVs) induced by flip-flops of lipids using coarse-grained molecular dynamics simulations. In the case of single-component SUVs composed of zero spontaneous curvature lipids (ZLs), the flip-flop of ZLs deformed stomatocyte-shaped SUVs into an oblate shape, whereas pear-shaped SUVs were deformed into a prolate shape. These two equilibrium shapes comply with the local minima of elastic energy. In the case of binary vesicles composed of ZLs and negative spontaneous curvature lipids (NLs), the vesicle deformation pathway depended on the initial NL distribution in the bilayer. If the initial difference in the NL concentration between the outer and inner leaflets was small, the flip-flop of ZLs and NLs rapidly deformed pear-shaped SUVs into an equilibrium prolate shape. On the other hand, when NLs were localised in the inner leaflet, the flip-flop of ZLs and NLs deformed pear-shaped SUVs into a limiting shape and then induced vesicle division. Because the flip-flop rate of NLs is much faster than that of ZLs, the total free energy was first relaxed by the flip-flop of NLs and then by that of ZLs. This kinetic effect is responsible for the observed vesicle division induced by flip-flops.

中文翻译：

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脂质分子触发器引起的囊泡变形和分裂

我们使用粗粒度分子动力学模拟研究了由脂质触发器引起的小单层囊泡 (SUV) 的变形。在由零自发曲率脂质 (ZLs) 组成的单组分 SUV 的情况下，ZL 的触发器将口孔细胞形状的 SUV 变形为扁圆形，而梨形 SUV 变形为扁长形状。这两个平衡形状符合弹性能的局部最小值。在由 ZL 和负自发曲率脂质 (NL) 组成的二元囊泡的情况下，囊泡变形途径取决于双层中的初始 NL 分布。如果外叶和内叶之间 NL 浓度的初始差异很小，则 ZL 和 NL 的触发器迅速将梨形 SUV 变形为平衡的长条形。另一方面，当 NLs 位于内叶时，ZLs 和 NLs 的触发器将梨形 SUV 变形为限制形状，然后诱导囊泡分裂。由于 NLs 的触发器速率比 ZLs 快得多，总自由能首先被 NLs 的触发器松弛，然后被 ZLs 的触发器松弛。这种动力学效应是由触发器诱导的观察到的囊泡分裂的原因。