MODEL MEMBRANES DISPLAYING COEXISTING LIQUID ORDERED AND DISORDERED PHASES

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。为了评估细胞质膜的raft假说的有效性，我们检测了脑鞘磷脂(SPM) /二油基磷脂酰胆碱(DOPC)/胆固醇模型膜系统中液体有序相（Lo）和液体无序相（Ld）的动力学和平衡。使用已知的脂质体系相图，其中包含Lo和Ld相的单相区和两相共存区之间的相边界，以及ESR光谱拟合方法(使用自旋标记ESR确定共存膜相系线的新方法，y - w。蒋，赵建军，吴建军，yyshimoyama， G.W. Feigenson， J.H. Freed，生物物理学报，168,99 -105,2005)从边界光谱的线性叠加中确定一条通过Lo+Ld共存区域的线。对于这种三重脂质系统，许多对Lo和Ld相组成可以在平衡状态下共存，因此线是模拟筏的必要条件，因为它们告诉我们哪些相组成共存，因此哪对组成最适合模拟质膜。如果在SPM/DOPC/胆固醇模型系统中观察到的Lo和Ld相在物理上与raft结构域相似，那么通过ESR光谱拟合确定的模型膜中自旋探针的动态参数应该与在质膜中相同探针的动态参数相似。这是正确的，从链标记自旋探针在一条线的边界组成中获得的动态参数与从活细胞中获得的动态参数相比非常好（ESR光谱表征活细胞质膜中的共存域，M.J. Swamy， L. Ciani， M. Ge， A.K. Smith， D. Holowka， B. Baird, and J.H. Freed, Biophys）。[j] .农业科学，2006,(2)。对Lo和Ld相平衡的更广泛的分析以及模型和真实质膜之间的动态比较将需要确定Lo+Ld相共存区域的整套线。

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.