Energetics of Channel-Bilayer Interactions

描述（由申请人提供）：膜蛋白功能受宿主双分子层脂质组成变化的调节。这一规律虽然已经确立，但仍然是一个谜，因为许多术语被用来描述其机制基础：双分子层流动性的变化；双层压缩能或曲率挫折能的变化，可合并为双层变形能；侧压分布或脂质堆积应力的变化；双层自由体积的变化；双层刚度的变化。双层流动性的变化不可能是主要机制，因为它们不能解释不同蛋白质构象之间平衡分布的变化。其余的描述符代表了参数化双层形成脂质之间以及脂质与嵌入蛋白之间相互作用的不同方法。提出的研究的目的是建立一个能量框架来描述膜跨越蛋白与其宿主双分子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-双分子层相互作用。该项目基于弹性双分子层的概念，其中膜蛋白经历构象变化，扰乱相邻的双分子层。这种扰动会产生能量损失，从而导致蛋白质构象变化的总自由能差。因此，蛋白质-双层疏水偶联导致蛋白质功能随脂质双层材料性质（厚度、脂质固有曲率和双层弹性压缩和弯曲模量）的变化而变化，脂质双层成为膜蛋白功能的变构调节剂。双层弹性性能的变化可以用一种恢复力来表征，这种恢复力拉动嵌入通道以使双层变形能最小化。这种力的变化可以使用双层嵌入传感器来测量。这些实验将解决以下问题。弹性双层模型在预测通道-双层双层相互作用的能量成本方面有多好？能应用于多组分脂质双分子层吗？这将使用磷脂（单独或组合）进行检查，磷脂形成厚度和脂质固有曲率不同的双层。小的两亲分子，如游离脂肪酸、抗菌肽和其他膜活性分子如何改变脂质双分子层材料性质和膜蛋白功能？这将通过探索选择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进行检查。PI(4,5)P2（和其他磷酸肌苷）能否通过局部改变双层材料性质来改变膜蛋白功能？这将使用gramicidin类似物与适当设计的磷酸肌苷结合域进行检查。通道-双层疏水错配能否驱动双层跨越通道之间的横向关联？这将通过检查嵌入不同厚度的双层中不同长度的双管通道的相对稳定性来研究。公共卫生相关性：拟议的研究将检查重要分子，如多不饱和脂肪酸（PUFAs），如何改变脂质双分子层性质，从而改变膜蛋白功能。该实验方法基于弹性双分子层的概念，通过与嵌入的膜蛋白的疏水偶联来调节膜蛋白的功能。吸附PUFAs等膜活性化合物可改变双层弹性，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.