Energetics of Channel-Bilayer Interactions

描述(由申请人提供)：膜蛋白功能由宿主双层的脂质组成的变化来调节。这一规则虽然已经确立，但从用于描述其机理基础的许多术语来看，仍然是一个谜：双分子层流动性的变化；双分子层压缩或曲率受挫能的变化，它们可以合并到双分子层变形能中；侧向压力分布或脂质填充应力的变化；双分子层自由体积的变化；双分子层硬度的变化。双层流动性的变化不是主要机制，因为它们不能解释不同蛋白质构象之间平衡分布的变化。剩下的描述符代表了不同的方法来参数化形成双层的脂类之间的相互作用以及脂类和嵌入的蛋白质之间的相互作用。这项研究的目的是建立一个能量框架来描述跨膜蛋白与其宿主双层之间疏水偶联的功能后果，并评估如何从药理学上操纵膜蛋白-双层相互作用。该项目基于弹性双层的概念，在弹性双层中，膜蛋白发生构象变化，扰乱相邻的双层。这种扰动会产生能量成本，从而导致蛋白质构象变化的总体自由能差异。因此，蛋白质-双层疏水偶联导致蛋白质功能随脂双层材料性质(厚度、脂质本征曲率和双层弹性压缩和弯曲模数)的变化而变化，从而成为膜蛋白功能的变构调节器。双层弹性性质的变化可以通过拉动嵌入通道以最小化双层变形能量的恢复力来表征。这种力的变化可以使用双层埋入传感器来测量。这些实验将解决以下问题。弹性双层模型在预测通道-双层相互作用的能量成本方面有多好？它能应用于多组分脂双层吗？这将使用磷脂(单独或组合)进行检查，磷脂形成的双层在厚度和脂质固有曲率上不同。小分子两亲性物质，如游离脂肪酸、抗菌肽和其他膜活性分子是如何改变脂双层材料的性质和膜蛋白功能的？这将通过探测选定的药物如何改变双分子层性质，并将这些信息与更复杂的系统联系起来来检验。PI(4，5)P2(和其他磷脂酰肌醇)能否通过双层材料性质的局部改变改变膜蛋白功能？这将使用带有适当设计的磷脂酰肌醇结合域的革兰西丁类似物进行研究。通道-双层疏水失配是否会驱动双分子层通道之间的横向关联？这将通过检查嵌入在不同厚度的双层中的不同长度的双管通道的相对稳定性来研究。与公共健康相关：拟议的研究将检验多不饱和脂肪酸(PUFAs)等重要分子如何改变脂质双层性质，从而改变膜蛋白的功能。实验方法基于弹性双层的概念，弹性双层通过疏水偶联嵌入的膜蛋白来调节膜蛋白的功能。多不饱和脂肪酸和其他膜活性物质的吸附可以改变膜的弹性，这为膜蛋白功能的改变提供了机制基础。

DESCRIPTION (provided by applicant): Membrane protein function is regulated by changes in the lipid composition of the host bilayer. This regulation, though well-established, remains enigmatic as evident by the many terms that are used to describe its mechanistic basis: changes in bilayer fluidity; changes in bilayer compression or curvature frustration energies, which can be combined into the bilayer deformation energy; changes in lateral pressure profile or lipid packing stress; changes in bilayer free volume; changes in bilayer stiffness. Changes in bilayer fluidity cannot be a major mechanism, as they cannot account for changes in the equilibrium distribution among different protein conformations. The remaining descriptors represent different approaches to parameterize the interactions among bilayer-forming lipids and between the lipids and the embedded proteins. The objective of the proposed studies is to develop an energetic framework for describing the functional consequences of the hydrophobic coupling between membrane-spanning proteins and their host bilayer, and to evaluate how membrane protein-bilayer interactions can be manipulated pharmacologically. The project is based on the notion of an elastic bilayer, in which membrane proteins undergo conformational changes that perturb the adjacent bilayer. This perturbation incurs an energetic cost that contributes to the overall free energy difference of the protein conformational changes. The protein-bilayer hydrophobic coupling therefore causes protein function to vary with changes in lipid bilayer material properties (thickness, lipid intrinsic curvature and the bilayer elastic compression and bending moduli), and the lipid bilayer becomes an allosteric regulator of membrane protein function. Changes in bilayer elastic properties can be characterized in terms of a restoring force that pulls on the embedded channel to minimize the bilayer deformation energy. Changes in this force can be measured using bilayer-embedded for transducers. The experiments will address the following questions. How good is the elastic bilayer model in predicting the energetic cost of channel-bilayer bilayer interactions? Can it be applied to multi-component lipid bilayers? This will be examined using phospholipids (alone or in combination), which form bilayers that differ in thickness and lipid intrinsic curvature. How do small amphiphiles, such as free fatty acids, antimicrobial peptides and other membrane-active molecules alter lipid bilayer material properties and membrane protein function? This will be examined by probing how selected drugs alter bilayer properties, and relating this information to more complex systems. Can PI(4,5)P2 (and other phosphoinositides) alter membrane protein function through local changes in bilayer material properties? This will be examined using gramicidin analogues with appropriately designed phosphoinositide-binding domains. Can the channel-bilayer hydrophobic mismatch drive a lateral association between bilayer-spanning channels? This will be studied by examining the relative stabilization of double- barreled channels of different lengths imbedded in bilayers of different thicknesses. PUBLIC HEALTH RELEVANCE: The proposed studies will examine how important molecules, such as poly-unsaturated fatty acids (PUFAs), alter lipid bilayer properties and thereby membrane protein function. The experimental approach is based on the notion of an elastic bilayer, which contributes to the regulation of membrane protein function through hydrophobic coupling to the embedded membrane proteins. The bilayer elasticity can be altered by the adsorption of PUFAs and other membrane-active compounds, which provides a mechanistic basis for the changes in membrane protein function.