Beck Erlach Markus, Koehler Joerg, Moeser Beate, Horinek Dominik, Kremer Werner, Kalbitzer Hans Robert
Institute of Biophysics and Physical Biochemistry and Centre of Magnetic Resonance in Chemistry and Biophysics, University of Regensburg , 93040 Regensburg, Germany.
J Phys Chem B. 2014 May 29;118(21):5681-90. doi: 10.1021/jp502664a. Epub 2014 May 19.
NMR chemical shift analysis is a powerful method to investigate local changes in the environment of the observed nuclear spin of a polypeptide that are induced by application of high hydrostatic pressure. Usually, in the fast exchange regime, the pressure dependence of chemical shifts is analyzed by a second order Taylor expansion providing the first- and second-order pressure coefficient B1 and B2. The coefficients then are interpreted in a qualitative manner. We show here that in a two-state model, the ratio of B2/B1 is related to thermodynamic parameters, namely the ratio of the difference of compressibility factors Δβ' and partial molar volumes ΔV. The analysis is applied to the random-coil model peptides Ac-Gly-Gly-Xxx-Ala-NH2, with Xxx being one of the 20 proteinogenic amino acids. The analysis gives an average Δβ'/ΔV ratio of 1.6 GPa(-1) provided the condition |ΔG(0)| ≪ 2RT holds for the difference of the Gibbs free energies (ΔG(0)) of the two states at the temperature (T0) and the pressure (p0). The amide proton and nitrogen B2/B1 of a given amino acid Xxx are strongly correlated, indicating that their pressure-dependent chemical shift changes are due to the same thermodynamic process. As a possible physical mechanism providing a two-state model, the hydrogen bonding of water with the corresponding amide protein was simulated for isoleucine in position Xxx. The obtained free energy could satisfy the relation |ΔG(0)| ≪ 2RT. The derived relation was applied to the β-amyloid peptide Aβ and the phosphocarrier protein HPr from S. carnosus. For the transition of state 1 to state 2' of Aβ, the derived relation of B2/B1 to Δβ'/ΔV can be confirmed experimentally. The HPr protein is characterized by substantially higher negative B2/B1 values than those found in the tetrapeptides with an average value of approximately -5.1 GPa(-1) (Δβ'/ΔV of 5.1 GPa(-1) provided |ΔG(0)| ≪ 2RT holds). Qualitatively, the B2/B1 ratio can be used to predict regions of the HPr protein involved in the interaction with enzyme I or HPr-kinase/phosphatase.
核磁共振化学位移分析是一种强大的方法，用于研究在高静水压力作用下多肽中被观测核自旋所处环境的局部变化。通常，在快速交换机制下，化学位移的压力依赖性通过二阶泰勒展开进行分析，从而得到一阶和二阶压力系数B1和B2。然后对这些系数进行定性解释。我们在此表明，在两态模型中，B2/B1的比值与热力学参数相关，即压缩因子差值Δβ'与偏摩尔体积差值ΔV的比值。该分析应用于随机卷曲模型肽Ac-Gly-Gly-Xxx-Ala-NH2，其中Xxx为20种蛋白质ogenic氨基酸之一。若在温度（T0）和压力（p0）下两态的吉布斯自由能差值（ΔG(0)）满足|ΔG(0)| ≪ 2RT这一条件，则分析得出平均Δβ'/ΔV比值为1.6 GPa(-1)。给定氨基酸Xxx的酰胺质子和氮的B2/B1高度相关，表明其与压力相关的化学位移变化是由同一热力学过程引起的。作为提供两态模型的一种可能物理机制，对Xxx位置的异亮氨酸模拟了水与相应酰胺蛋白的氢键作用。所获得的自由能能够满足|ΔG(0)| ≪ 2RT这一关系。将推导得出的关系应用于β-淀粉样肽Aβ和来自肉葡萄球菌的磷酸载体蛋白HPr。对于Aβ从状态1到状态2'的转变，B2/B1与Δβ'/ΔV的推导关系可通过实验得到证实。HPr蛋白的特征在于其B2/B1值比在四肽中发现的负值要高得多，其平均值约为 -5.1 GPa(-1)（若|ΔG(0)| ≪ 2RT成立，则Δβ'/ΔV为5.1 GPa(-1)）。定性地说，B2/B1比值可用于预测HPr蛋白中参与与酶I或HPr激酶/磷酸酶相互作用的区域。
