Markvoort A J, Smeijers A F, Pieterse K, van Santen R A, Hilbers P A J
Departments of Biomedical Engineering and Chemical Engineering, TU Eindhoven, Postbus 513, 5600 MB Eindhoven, The Netherlands.
J Phys Chem B. 2007 May 24;111(20):5719-25. doi: 10.1021/jp068277u. Epub 2007 Apr 11.
Shape transformations and topological changes of lipid vesicles, such as fusion, budding, and fission, have important chemical physical and biological significance. In this paper, we study the fission process of lipid vesicles. Two distinct routes are considered that are both based on an asymmetry of the lipid distribution within the membrane. This asymmetry consists of a nonuniform distribution of two types of lipids. In the first mechanism, the two types of lipids are equally distributed over both leaflets of the membrane. Phase separation of the lipids within both leaflets, however, results in the formation of rafts, which form buds that can split off. In the second mechanism, the asymmetry consists of a difference in composition between the two monolayers of the membrane. This difference in composition yields a spontaneous curvature, reshaping the vesicle into a dumbbell such that it can split. Both pathways are studied with molecular dynamics simulations using a coarse-grained lipid model. For each of the pathways, the conditions required to obtain complete fission are investigated, and it is shown that for the second pathway, much smaller differences between the lipids are needed to obtain fission than for the first pathway. Furthermore, the lipid composition of the resulting split vesicles is shown to be completely different for both pathways, and essential differences between the fission pathway and the pathway of the inverse process, i.e., fusion, are shown to exist.
脂质囊泡的形状转变和拓扑变化，如融合、出芽和裂变，具有重要的化学物理和生物学意义。在本文中，我们研究脂质囊泡的裂变过程。考虑了两种不同的途径，它们都基于膜内脂质分布的不对称性。这种不对称性由两种脂质的不均匀分布组成。在第一种机制中，两种脂质均匀分布在膜的两个小叶上。然而，两个小叶内脂质的相分离导致筏的形成，筏形成可以分裂出去的芽。在第二种机制中，不对称性由膜的两个单层之间的组成差异组成。这种组成差异产生自发曲率，将囊泡重塑成哑铃状，使其能够分裂。使用粗粒度脂质模型通过分子动力学模拟研究了这两种途径。对于每种途径，研究了获得完全裂变所需的条件，结果表明，对于第二种途径，获得裂变所需的脂质差异比第一种途径小得多。此外，结果表明，两种途径产生的分裂囊泡的脂质组成完全不同，并且裂变途径与逆过程即融合途径之间存在本质差异。
