Beck Erlach Markus, Koehler Joerg, Crusca Edson, Munte Claudia E, Kainosho Masatsune, Kremer Werner, Kalbitzer Hans Robert
Institute of Biophysics and Physical Biochemistry and Centre of Magnetic Resonance in Chemistry and Biomedicine, University of Regensburg, 93040, Regensburg, Germany.
Institute of Chemistry, São Paulo State University (UNESP), Araraquara, 14800-060, Brazil.
J Biomol NMR. 2017 Oct;69(2):53-67. doi: 10.1007/s10858-017-0134-5. Epub 2017 Sep 14.
For evaluating the pressure responses of folded as well as intrinsically unfolded proteins detectable by NMR spectroscopy the availability of data from well-defined model systems is indispensable. In this work we report the pressure dependence of C chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH (Xxx, one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of a number of nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The size of the polynomial pressure coefficients B and B is dependent on the type of atom and amino acid studied. For H, N and C the first order pressure coefficient B is also correlated to the chemical shift at atmospheric pressure. The first and second order pressure coefficients of a given type of carbon atom show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure also are weakly correlated. The downfield shifts of the methyl resonances suggest that gauche conformers of the side chains are not preferred with pressure. The valine and leucine methyl groups in the model peptides were assigned using stereospecifically C enriched amino acids with the pro-R carbons downfield shifted relative to the pro-S carbons.
为了评估通过核磁共振光谱法可检测到的折叠蛋白以及内在无序蛋白的压力响应，来自定义明确的模型系统的数据是必不可少的。在这项工作中，我们报告了受保护的四肽Ac-Gly-Gly-Xxx-Ala-NH（Xxx为20种标准氨基酸之一）中侧链原子的C化学位移与压力的关系。与预期相反，许多原子核的化学位移在0.1至200MPa范围内对压力呈非线性依赖。多项式压力系数B和B的大小取决于所研究的原子和氨基酸类型。对于H、N和C，一阶压力系数B也与大气压下的化学位移相关。给定类型碳原子的一阶和二阶压力系数显示出显著的线性相关性，这表明不同氨基酸中核磁共振可观测到的压力效应至少部分具有相同的物理原因。与此观察结果一致，在化学结构中直接相邻的原子核的二阶系数大小也存在弱相关性。甲基共振的向低场位移表明，侧链的gauche构象在压力下不受青睐。使用立体特异性富集C的氨基酸对模型肽中的缬氨酸和亮氨酸甲基进行了归属，其中pro-R碳相对于pro-S碳向低场位移。
