Barfield Michael
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
J Am Chem Soc. 2002 Apr 17;124(15):4158-68. doi: 10.1021/ja012674v.
A study is presented of the structural dependencies for scalar J-coupling and the amide donor (1)H chemical shifts in the hydrogen bonding regions of proteins. An analysis of the interactions between the donor hydrogen and acceptor oxygen orbitals in an N-H...O=C moiety suggests that there are three major structural factors for (15)N-(13)C coupling across hydrogen bonds: (1) the H...O' internuclear separation r(HO)('), (2) the H...O'=C' angle theta(2), and (3) indirect contributions involving the oxygen loan pair electrons should lead to a dependence on the H...O'=C'-N' dihedral angle rho. Density functional theory (DFT) and finite perturbation theory (FPT) were used to obtain the Fermi contact (FC) contributions to interresidue coupling in formamide dimers with systematic variation of these structural parameters. The computed (h3)J(NC)(') exhibit good correlations with cos(2) theta;(2) combined with an exponential dependence on r(HO)('). The correlation is further improved by including a dependence on the dihedral angle rho. For each of the 34 H-bonds having observable interresidue coupling in the immunoglobulin binding domain of streptococcal protein G, a formamide dimer was generated from the crystallographic structure with energy-optimized donor H-atom positions. The computed coupling constants are in reasonable agreement with the experimental, and there are excellent correlations with the simple equations involving theta;(2) and r(HO) if alpha-helix and beta-sheet regions are treated separately. This dichotomy is removed by introducing the dependence on the dihedral angle rho. Justification for the use of formamide dimers is provided by almost identical interresidue coupling constants for larger sequences extracted from the X-ray structure. The amide donor (1)H chemical shifts, which were based on DFT and GIAO (gauge including atomic orbital) methods, are in poorer agreement with the experimental data but exhibit excellent correlation with r(HO)('), theta(2), and rho.
本文介绍了一项关于蛋白质氢键区域中标量 J 耦合和酰胺供体氢化学位移的结构依赖性研究。对 N-H...O=C 部分中供体氢与受体氧轨道之间相互作用的分析表明，氢键上 15N-13C 耦合存在三个主要结构因素：(1) H...O' 核间距 r(HO)'；(2) H...O'=C' 角 θ₂；(3) 涉及氧孤对电子的间接贡献应导致对 H...O'=C'-N' 二面角 ρ 的依赖性。利用密度泛函理论(DFT)和有限微扰理论(FPT)，通过系统改变这些结构参数，得到了甲酰胺二聚体中残基间耦合的费米接触(FC)贡献。计算得到的³J(NC)' 与 cos²θ₂ 表现出良好的相关性，并与 r(HO)' 呈指数依赖关系。通过纳入对二面角 ρ 的依赖性，相关性进一步提高。对于链球菌蛋白 G 免疫球蛋白结合域中具有可观测残基间耦合的 34 个氢键中的每一个，从晶体结构生成了甲酰胺二聚体，并对供体氢原子位置进行了能量优化。计算得到的耦合常数与实验结果合理吻合，如果分别处理 α 螺旋和 β折叠区域，则与涉及 θ₂ 和 r(HO) 的简单方程具有极好的相关性。通过引入对二面角 ρ 的依赖性，消除了这种二分法。从 X 射线结构中提取的较大序列的几乎相同的残基间耦合常数，为使用甲酰胺二聚体提供了依据。基于 DFT 和 GIAO（含原子轨道规范）方法的酰胺供体氢化学位移与实验数据的吻合度较差，但与 r(HO)'、θ₂ 和 ρ 表现出极好的相关性。
