MODEL MEMBRANES DISPLAYING COEXISTING LIQUID ORDERED AND DISORDERED PHASES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 为了评价细胞质膜RAFT假说的正确性，我们研究了脑-神经鞘磷脂(SPM)/二油酰磷脂酰胆碱(DOPC)/胆固醇模型膜体系中液体有序(LO)和液体无序(LD)相的动力学和平衡。利用已知的包含LO和LD相的单相区和两相共存区域的相图和ESR光谱拟合法(利用自旋标记ESR确定共存膜相中的联络线的新方法，Y.-W.Chiang，J.赵，J.Wu，Y.Shimyama，G.W.Feigenson，J.H.Freed，BiPhysica-Biochimica Acta 1668，99-105,2005)，从边界光谱的线性叠加确定了一条穿过Lo LD共存区域的Tiline。对于这种三元脂质体系，许多LO和LD相组成可以在平衡状态下共存，因此用梯度线来模拟浮筏是必要的，因为它们告诉我们哪些相组成共存，从而哪对相组成最好地模拟质膜。如果在SPM/DOPC/胆固醇模型体系中观察到的LO和LD相在物理上类似于RAFT结构域，那么由ESR光谱拟合确定的模型膜中的自旋探针的动力学参数应该与同一探针在质膜中的动力学参数相似。这一点被发现是正确的，因为到目前为止所确定的一个Tieline的边界成分处的链标记自旋探针的动态参数与来自活细胞中相同自旋探针的动态参数(通过ESR光谱表征的活细胞的质膜中的共存结构域，M.J.Swamy，L.Ciani，M.GE，A.K.Smith，D.Holowka，B.Baird，和J.H.Freed，BiPhys)相比非常好。J.90,4452-4465,2006)。要对LO和LD相平衡进行更广泛的分析，并在模型和实际质膜之间进行动态比较，将需要确定LO-LD相共存区域的整套倾斜线。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. To assess the validity of the raft hypothesis for the cellular plasma membrane we examined both the dynamics and equilibria of liquid-ordered (Lo) and liquid-disordered (Ld) phases in the brain-sphingomyelin (SPM) /dioleoylphosphatidylcholine (DOPC)/cholesterol model membrane system. Using the known phase diagram for this lipid system containing the phase boundary between the one-phase regions and the two-phase coexistence region of the Lo and Ld phases and an ESR spectral fitting method (New Method for Determining Tie-lines in Coexisting Membrane Phases using Spin-label ESR, Y.-W. Chiang, J. Zhao, J. Wu, Y. Shimoyama, G.W. Feigenson, J.H. Freed, Biophysica-Biochimica Acta 1668, 99-105,2005) from the linear superposition of boundary spectra, we determined one tieline thru the Lo+Ld coexistence region. Many pairs of Lo and Ld phase compositions can coexist at equilibrium for this ternary lipid system, so tielines are necessary to model rafts because they tell us which phase compositions coexist and therefore which pair of compositions best model the plasma membrane. If the Lo and Ld phases observed in the SPM/DOPC/cholesterol model system are physically similar to raft domains, then the dynamic parameters of spin probes in the model membranes determined from ESR spectral fitting should be similar to those of the same probe in plasma membranes. This was found to be true in that dynamic parameters from chain-labeled spin probes at the boundary compositions of the one tieline so far determined compared very well with dynamic parameters from the same spin probes in live cells (Coexisting Domains in the Plasma Membranes of Live Cells Characterized by ESR Spectroscopy, M.J. Swamy, L. Ciani, M. Ge, A.K. Smith, D. Holowka, B. Baird, and J.H. Freed, Biophys. J. 90, 4452-4465, 2006). A more extensive analysis of Lo and Ld phase equilibria and dynamic comparison between model and real plasma membranes will require the determination of the entire set of tielines for the Lo+Ld phase coexistence region.