Liu Jian, Qi Shuyan, Groves Jay T, Chakraborty Arup K
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Phys Chem B. 2005 Oct 27;109(42):19960-9. doi: 10.1021/jp053562j.
Lipid rafts are sphingolipid- and cholesterol-enriched domains on cell membranes that have been implicated in many biological functions, especially in T lymphocytes. We used a field theory to examine the forces underlying raft formation on resting living cell membranes. We find that it is difficult to reconcile the observed size of rafts on living cell membranes ( approximately 100 nm) with a mechanism that involves coupling between spontaneous curvature differences and concentration fluctuations. Such a mechanism seems to predict raft domain sizes that are larger and commensurate with those observed on synthetic membranes. Therefore, using a Poisson-Boltzmann approach, we explore whether electrostatic forces originating from transmembrane proteins and net negative charges on cell membranes could play a role in determining the raft size in living cell membranes. We find that a balance among the intrinsic tendency of raft components to segregate, the line tension, and the effective dipolar interactions among membrane constituents leads to a stable phase with a characteristic length scale commensurate with the observed size of rafts on living cell membranes. We calculate the phase diagram of a system in which these three types of forces are important. In a certain region of the parameter space, an interesting phase with mosaic-like morphology consisting of an intertwined pattern of raft and nonraft domains is predicted. Experiments that could further assess the importance of dipolar interactions for lateral organization of the components on multiple length scales in membranes are suggested.
脂筏是细胞膜上富含鞘脂和胆固醇的结构域，与许多生物学功能有关，尤其是在T淋巴细胞中。我们使用场论来研究静息活细胞膜上筏形成的潜在作用力。我们发现，很难将活细胞膜上观察到的筏的大小（约100纳米）与一种涉及自发曲率差异和浓度波动之间耦合的机制相协调。这样一种机制似乎预测的筏结构域大小更大，且与在合成膜上观察到的大小相当。因此，我们使用泊松-玻尔兹曼方法，探讨源自跨膜蛋白和细胞膜上净负电荷的静电力是否在决定活细胞膜上筏的大小中发挥作用。我们发现，筏成分的内在分离倾向、线张力和膜成分之间的有效偶极相互作用之间的平衡导致了一个具有与活细胞膜上观察到的筏大小相当的特征长度尺度的稳定相。我们计算了这三种力起重要作用的系统的相图。在参数空间的某个区域，预测了一种有趣的相，其具有由筏和非筏结构域的交织图案组成的马赛克状形态。还提出了可以进一步评估偶极相互作用对膜中多个长度尺度上成分横向组织重要性的实验。
