Understanding the functional activation of G protein-coupled receptors (GPCRs) in the context of their lipid bilayer environment

人类是由数百万个细胞组成的。为了维持生命，这些细胞需要能够协同工作。每个细胞都有自己的机制，并被一层不透水的膜包围，形成物理边界。这种膜由脂质双分子层组成，其中嵌入了大量不溶于水的蛋白质，即所谓的膜蛋白。这些细胞是通过细胞膜传递所需营养物质、能量和信息所必需的。为了以协调的方式工作，细胞需要能够调整自己以适应周围环境的变化。这需要跨膜双分子层传递环境变化的能力。大约有800种膜内蛋白的大家族负责完成这一任务。这些所谓的G蛋白偶联受体（gpcr）具有感知化学物质、多肽和蛋白质形式的广泛细胞外刺激的能力，例如气味、信息素、神经递质、激素、光（以及其他），并将它们的存在传递给细胞内部。作为细胞传感器，gpcr在广泛的正常、生理和疾病相关过程的调节中起着关键作用。它们位于细胞表面，已经成为许多现有药物的靶标。然而，为了解决更多的疾病或改善现有的治疗方法，进一步发展这一技术有很大的潜力，有望在未来显著改善健康状况。为了实现这一目标，迫切需要更好地了解gpcr的功能。这通常涉及在分子水平上获取这些蛋白质的信息，化学家和生物学家正在使用一系列复杂的方法来产生这种见解。对于越来越多的gpcr，最近以静态快照图片的形式可视化这些高度不稳定和难以处理的蛋白质的结构方面成为可能。基于这些，人们会假设gpcr的功能是简单的开/关开关。然而，gpcr是高度可移动、可变形的蛋白质，这一标志性特征是其功能的核心。因此，随着简单的开/关图像逐渐被描述gpcr为变阻器（即连续调节器）的图像所取代，许多问题仍有待回答。在我们的建议中，我们将使用一种称为b1肾上腺素能受体（b1AR）的特殊GPCR来研究这些受体的动态性质。这种受体在心脏功能的调节中起着重要作用，与许多疾病有关，是著名的受体阻滞剂药物的靶点。为了了解GPCR功能的动态性质，我们将模拟自然细胞膜环境，并将受体嵌入类似于脂质双层筏的小颗粒中。然后，我们将使用一种称为核磁共振（NMR）光谱学的技术来研究这些蛋白质的形状变化特性如何影响它们的功能。利用这种小的膜双分子层颗粒，可以使我们在现实条件下研究b1AR，并重点研究脂质环境对GPCR功能的作用。核磁共振波谱将使我们深入了解这种受体如何与一系列与受体偶联的蛋白质相互作用，以及GPCR感知的初始信号如何从细胞外部穿过膜传递到细胞内部。我们将能够研究由于技术原因其他调查方法无法进入的受体区域，这是特别有价值的。我们的研究将提高我们对这种受体如何工作的理解，并将为开发新药奠定基础。虽然我们的一些发现将是针对b1AR受体的，但我们预计许多发现也将促进我们对gpcr如何工作的一般理解。

Human beings are made up of millions of cells. To sustain life these cells need to be able to work together. Each cell has its own machinery and is surrounded by a water-impermeable membrane forming a physical boundary. This membrane consists of a lipid bilayer into which a large number of water-insoluble proteins are embedded, so-called membrane proteins. These are essential for transmitting required nutrients, energy and information across the membrane. To work in a coordinated fashion, cells need to be able to adjust themselves to changes in their surroundings. This requires the ability to communicate environmental variations across the membrane bilayer. A large family of ca. 800 membrane embedded proteins is tasked to do this. These so-called G protein-coupled receptors (GPCRs) have the ability to sense the presence of a wide range of extracellular stimuli in the form of chemicals, peptides and proteins, for example odorants, pheromones, neurotransmitters, hormones, light (amongst others) and to communicate their presence to the cell interior. As cellular sensors, GPCRs are key players in the regulation of a wide range of normal, physiological and disease-related processes. Located on the cell surface they are already targeted by many of the currently available drugs. However, there is vast potential to develop this further in order to tackle many more diseases or improve existing treatments, with the promise to lead to dramatic improvements in health in the future. To achieve this, there is an urgent need to obtain a better understanding of how GPCRs function. Typically this involves obtaining information on these proteins at a molecular level, and chemists and biologists are using a range of sophisticated methodologies that generate such insight. For an increasing number of these GPCRs it has recently become possible to visualize the structural aspects of these highly unstable and difficult to handle proteins in the form of static snapshot pictures. Based on these, one would assume that GPCRs function as simple on/off switches. However, GPCRs are highly mobile, shape-shifting proteins and this trademark characteristic lies at the heart of their function. Accordingly, many questions remain to be answered as the simple on/off picture is gradually replaced by one portraying GPCRs as rheostats i.e. continuous regulators.In our proposal we will investigate the dynamic nature of these receptors using a particular GPCR called b1 adrenergic receptor (b1AR). This receptor plays an important role in the regulation of heart function, is involved in many diseases and is targeted by the famous beta blocker drugs. To understand the role of the dynamic nature for GPCR function we will mimic the natural cellular membrane environment and embed the receptor in small particles that resemble lipid bilayer rafts. We will then use a technique called nuclear magnetic resonance (NMR) spectroscopy to investigate how the shape-shifting properties of these proteins contribute to their function. Using such small membrane bilayer particles will allow us to study b1AR under realistic conditions and to focus on the role of the lipid environment for GPCR function. NMR spectroscopy will give us insight on how this receptor interacts with a range of proteins that couple to the receptor and how the initial signal sensed by the GPCR is transmitted from the cell exterior across the membrane to the inside of the cell. We will be able to study regions of the receptor that for technical reasons are inaccessible to other investigation methods, which is particularly valuable. Our study will improve our understanding of how this receptor works and will create a basis for the development of new drugs. While some of our findings will be specific to the b1AR receptor we are anticipating that many of the discoveries will also advance our general understanding of how GPCRs work.