Characterization of rare conformational states of proteins by combination of high-pressure X-raycrystallography with high-pressure NMR spectroscopy. Application to the small GproteinRas, its oncogenic mutants and its drug complexes.

高压核磁共振波谱（HPNMR）代表了一种强大的，仍在发展的方法来检测和表征罕见的“激发态”构象状态。这些状态在蛋白质的功能和折叠中起着重要的作用。HPNMR提供了它们的热力学参数，但只给出了有限分辨率的结构信息。高压大分子x射线晶体学（HPMX）是蛋白质科学中一种互补的新方法，基本上可以在高压下提供高分辨率的空间结构。作为一个重要且特征明确的信号转导系统的组成部分，我们将集中研究小g蛋白Ras（大鼠肉瘤）蛋白（Ras突变在超过30%的人类癌症中被发现发生突变）。它可以作为拟议项目中方法开发的良好表征模型，但新的热力学和结构见解也具有很高的医学重要性，因为它们可能有助于开发变构性Ras抑制剂。通过与GTP类似物GppNHp配合物的HPNMR，可以表征出在环境压力下共存的4种状态1(0)、1(T)、2(T)和3(T)。优先结合状态1(T)的小化合物可以变变地抑制效应物相互作用，因此原则上可以抑制致癌Ras突变体的增殖作用。本项目的主要目标是：(1)在CEST和弛驰色散测量等替代核磁共振方法的支持下，通过HPNMR对H-和K-Ras及其致癌突变体与GDP和GppNHp复合物中罕见的构象状态进行彻底的定量分析；(2)证明HPMX可以有效地捕获高压核磁共振光谱在溶液中鉴定的蛋白质的高能构象。(3)将观察到的核磁共振参数的压力响应与HPMX检测到的结构变化联系起来；(4)原则上，得到的高压晶体结构可以用于设计特异性的与稀有态结合的变构抑制剂。为了证明晶体和溶液的热力学相似态是否在结构上也相似，根据x射线结构反演了种群加权NOESY谱，并与不同压力下的实验溶液态NOESY谱进行了详细比较。初步实验表明，用小态特定化合物高压浸泡可能是一种通过晶体学获得稀有构象态的新方法。利用自制的高压跳变系统，对富同位素Ras蛋白进行二维瞬态p跳实验，研究其在不同状态下的动力学特性。本研究将辅以不同压力下的弛豫分散和化学交换饱和转移（CEST）实验。

High pressure NMR spectroscopy (HPNMR) represents a powerful, still developing method to detect and characterize rare 'excited' conformational states. These states play an essential role in function and folding of proteins. HPNMR provides their thermodynamic parameters but gives structural information with limited resolution only. High pressure macromolecular x-ray crystallography (HPMX) is a complementary new method in protein science that basically can provide highly resolved spatial structures at high pressures. As component of an important and well-characterized signal transduction system we will concentrate on the small G-Protein Ras (rat sarcoma) protein (Ras mutations are found mutated in more than 30 % of all human cancers). It serves as a well-characterized model for method development in the proposed project, but also novel thermodynamic and structural insights are from high medical importance since they may help with the development of allosteric Ras inhibitors. By HPNMR of Ras in complex with the GTP analog GppNHp four different states 1(0), 1(T), 2(T), and 3(T) could be thermodynamically characterized that coexist at ambient pressure. Small compounds that preferentially bind to state 1(T) can allosterically inhibit the effector interaction and thus in principle can suppress the proliferative effect of oncogenic Ras mutants. The main goals of this project are (1) a thorough quantitative analysis of the rare conformational states of H- and K-Ras and their oncogenic mutants in complex with GDP and GppNHp by HPNMR supported by alternative NMR methods such as CEST and relaxation dispersion measurements, (2) to prove that HPMX can efficiently trap high-energy conformers of proteins identified in solution by high-pressure NMR spectroscopy that were identified in solution by HPNMR, (3) to correlate the observed pressure response of NMR parameters with structural changes detected by HPMX, and (4) to show that in principle the obtained high-pressure crystallographic structures can be used to design specific allosteric inhibitors binding to rare states. For showing if the thermodynamically similar state sin crystal and solution are also structurally similar, population-weighted NOESY spectra are back calculated from the X-ray structures and are compared with the experimental solution state NOESY spectra at different pressures in detail. As preliminary experiments show high pressure soaking with small state specific compounds may represent a novel method to access rare conformational states by crystallography. The dynamics under pressure of the different states will be studied by 2D transient P-jump experiments on isotope enriched Ras protein with the high-pressure jump system developed by us. The study will be complemented by relaxation dispersion and chemical exchange saturation transfer (CEST) experiments at different pressures.