Domains in Biologically Relevant Lipid Membranes

生物学相关脂质膜中的结构域

• 批准号: RGPIN-2014-04934
• 负责人: Thewalt, Jenifer
• 金额: $ 2.55万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=566833
• 关键词: Domains; Biologically; Relevant; Lipid; Membranes

Cell membranes are complex assemblies of lipids and proteins held together by lipids' natural tendency to form bilayers. Membrane lipids have large structural variability and recent evidence suggests that many biological membranes contain domains, distinguishable by both composition and physical characteristics. These domains are often enriched in sphingolipids, which tend in isolation to have relatively high melting temperatures, and sterols such as cholesterol, but are extremely difficult to characterize in living systems due to their small size and dynamic nature. Based on work with ‘model’ membranes, i.e. membranes with defined composition, often protein-free, such domains are postulated to have a different physical state ("the liquid ordered phase"), where the lipids have a more conformationally ordered liquid crystalline structure than the surrounding membrane. Long-lived phase coexistence within a membrane strongly influences membrane character: local membrane thickness and curvature, diffusion of lipids and proteins within the membrane, interactions between lipids and proteins, and membrane protein function/flexibility could all be affected in cell membranes containing such domains. We will map out the fundamental interactions between phospholipids and sterols in model membranes designed to mimic the outer surface of cells. Many of these interactions are poorly understood even though they form the backdrop for the interplay among other cell membrane components. Deuterium nuclear magnetic resonance (NMR) is a powerful experimental approach to the study of phase or domain coexistence in membranes; different phases result in clearly distinguishable spectra, and the quantity of labeled lipid in a particular phase can be measured unambiguously. Importantly, deuterium NMR does not rely on large unnatural probes to monitor membrane domains, as even small amounts of such probes can modify domain properties. A new direction for us is monitoring the tendency of lipids used to manufacture specialized “lipid nanoparticles” (LNPs) to form non-bilayer phases. LNPs are used in gene therapy: they are taken up by the liver and then release short strands of RNA inside the cell. The release mechanism is thought to involve a transition from a typical bilayer to a different membrane morphology, consisting of tiny water-filled lipid cylinders, that has a distinct NMR signature. In collaboration with experts in the computer simulation of membrane structure, we will better understand the lipid qualities that favour the phase transition and in turn more accurately predict the mechanism of drug release. Knowledge gained from the proposed research will aid cell biologists investigating phenomena related to membrane domains, e.g. programmed cell death, protein localization and signaling, neuronal maturation and bacterial or viral infection. Cell physiologists will be able to use our work to better understand fast, non-genomic responses of tissues to active molecules, such as steroid hormones, in circulation. Finally, the membrane simulation community relies on reliable data about the structure and dynamics of lipids. Thus, our work will benefit a broad segment of the cell biological and biophysical research communities. In addition it will provide Canada with highly trained scientists whose knowledge will provide leadership to future industrial, medical and academic research.

细胞膜是由脂质和蛋白质通过脂质形成双层的天然倾向而保持在一起的复杂组件。膜脂具有很大的结构变异性，最近的证据表明，许多生物膜包含域，可通过组成和物理特性进行区分。这些结构域通常富含鞘脂和甾醇，鞘脂在分离时往往具有相对高的熔化温度，甾醇如胆固醇，但由于它们的小尺寸和动态性质，极难在生命系统中表征。基于对“模型”膜（即具有确定组成的膜，通常不含蛋白质）的研究，假定此类结构域具有不同的物理状态（“液体有序相”），其中脂质具有比周围膜更构象有序的液晶结构。膜内的长寿命相共存强烈影响膜特性：局部膜厚度和曲率、膜内脂质和蛋白质的扩散、脂质和蛋白质之间的相互作用以及膜蛋白功能/柔性都可能在含有此类结构域的细胞膜中受到影响。我们将绘制出磷脂和甾醇在模拟细胞外表面的模型膜之间的基本相互作用。这些相互作用中的许多都知之甚少，即使它们形成了其他细胞膜成分之间相互作用的背景。氘核磁共振（NMR）是研究膜中相或域共存的强大实验方法;不同的相导致清晰可辨的光谱，并且可以明确测量特定相中标记脂质的量。重要的是，氘NMR不依赖于大的非天然探针来监测膜结构域，因为即使是少量的这种探针也可以改变结构域的性质。我们的一个新方向是监测用于制造专门的“脂质纳米颗粒”（LNP）的脂质形成非双层相的趋势。LNP用于基因治疗：它们被肝脏吸收，然后在细胞内释放短链RNA。释放机制被认为涉及从典型的双层到不同的膜形态的过渡，由微小的充满水的脂质圆柱体组成，具有独特的NMR特征。通过与计算机模拟膜结构的专家合作，我们将更好地了解有利于相变的脂质质量，从而更准确地预测药物释放的机制。从拟议的研究中获得的知识将有助于细胞生物学家研究与膜结构域相关的现象，例如程序性细胞死亡，蛋白质定位和信号传导，神经元成熟和细菌或病毒感染。细胞生理学家将能够利用我们的工作来更好地了解组织对循环中的活性分子（如类固醇激素）的快速非基因组反应。最后，膜模拟社区依赖于有关脂质结构和动力学的可靠数据。因此，我们的工作将有利于细胞生物学和生物物理学研究社区的广泛部分。此外，它将为加拿大提供训练有素的科学家，他们的知识将为未来的工业，医学和学术研究提供领导。