Model Membrane Structure, Molecular Order, Fluctuations and Dynamics

这项研究计划的总体目标是提高我们对膜的物理特性如何影响其生物功能的理解。一个更直接的目标是了解这些物理性质如何影响并确定可用于研究膜的方法。我们进行精确实验测量的能力取决于膜的物理性质。例如，在荧光显微镜或核磁共振（NMR）光谱学中，分子运动的速率决定了我们是否能观察到任何东西。人们早就知道胆固醇能增厚双分子膜层，使其更有弹性。最近发现，质膜的高胆固醇含量使它们接近临界点，从而使局部膜成分波动。这可能会对膜功能产生重大影响。我们还在研究多肽作为模型蛋白如何影响模型膜中的这种行为，以及多肽本身如何受到关键行为的影响。此外，我们希望更多地了解小膜活性肽与膜之间的相互作用。我们研究的主要目的之一是找到可以进行精确物理测量的条件。我们在这个建议中概述了我们的计划，以研究多肽，脂质和胆固醇在模型膜中的相互作用。该计划的一部分涉及开发新的核磁共振技术，利用膜成分的特殊性：1)胆固醇诱导形成两种流体膜相；Ii)短链脂质，其包含在模型膜中可以使系统在外加磁场下自发定向；iii)多不饱和脂质，比饱和脂质具有更高的“流动性”，导致分子定向更快，因此在核磁共振实验中具有更高的分辨率。所有这些因素都可以用来优化实验设计。这一原理的一个重要例子是，我们能够获得高分辨率的1H魔角旋转核磁共振光谱，以便研究一类有趣的小肽在生理条件下与膜相互作用。这是可能的，因为流体膜中的分子围绕局部双层法线进行快速的轴对称重新定向。尽管谱线宽度仍然比在溶液中观察到的谱线宽度宽，但我们可以对它们进行分析，以获得有关整体相行为、分子结构和动力学的信息。

The overall aim of this research program is to improve our understanding of how the physical properties of membranes affect their biological function. A more immediate goal is to understand how these physical properties affect and determine the approaches which can be used to study membranes. Our ability to perform accurate experimental measurements depends on the physical properties of the membrane. For example, in fluorescence microscopy or in nuclear magnetic resonance (NMR) spectroscopy the rates of molecular motion determine whether or not we can actually observe anything at all. Cholesterol has long been known to thicken the membrane bilayer and to make it somewhat more resilient. More recently it has been found that the high cholesterol content of plasma membranes places them close to a critical point such that the local membrane composition fluctuates. This may turn out to have a significant impact on membrane function. We are also studying how the inclusion of peptides, as model proteins, affect this behaviour in model membranes and how the peptides themselves are affected by the critical behaviour. Furthermore, we want to learn more about the interaction between small membrane active peptides and the membrane.One of the principal aims of our research is to find conditions under which we can make accurate physical measurements. We outline in this proposal our program for studying the interactions of peptides, lipids and cholesterol in model membranes. Part of this program involves the development of new NMR techniques which take advantage of the special nature of the membrane components: i) cholesterol which induces the formation of two fluid membrane phases; ii) short chain lipids whose inclusion in a model membrane can cause the system to spontaneously orient within an applied magnetic field; iii) polyunsaturated lipids which are much more highly 'fluid' than the saturated lipids, resulting in more rapid molecular reorientation and, consequently, higher resolution in NMR experiments. All of these factors can be used to optimize experimental design. An important illustration of this principle is that we are able to obtain high resolution 1H magic angle spinning NMR spectra in order to study an interesting class of small peptides interacting with membranes under physiological conditions. This is possible because the molecules in a fluid membrane undergo rapid axially symmetric reorientation about the local bilayer normal. Even though the spectral linewidths are still broader than those observed in solution, we can analyse them to obtain information about the overall phase behaviour and the molecular structure and dynamics.