Laboratory of Physical Chemistry, ETH, Swiss Federal Institute of Technology, 8093 Zurich, Switzerland.
J Biomol NMR. 2012 Jul;53(3):223-46. doi: 10.1007/s10858-012-9634-5. Epub 2012 Jun 20.
Structural knowledge about proteins is mainly derived from values of observables, measurable in NMR spectroscopic or X-ray diffraction experiments, i.e. absorbed or scattered intensities, through theoretically derived relationships between structural quantities such as atom positions or torsional angles on the one hand and observable quantities such as squared structure factor amplitudes, NOE intensities or (3) J-coupling constants on the other. The standardly used relation connecting (3) J-couplings to torsional angles is the Karplus relation, which is used in protein structure refinement as well as in the evaluation of simulated properties of proteins. The accuracy of the simple and generalised Karplus relations is investigated using side-chain structural and (3) J (αβ)-coupling data for three different proteins, Plastocyanin, Lysozyme, and FKBP, for which such data are available. The results show that the widely used Karplus relations are only a rough estimate for the relation between (3) J (αβ)-couplings and the corresponding χ(1)-angle in proteins.
蛋白质的结构知识主要来自可观测值的值，这些值可在 NMR 光谱或 X 射线衍射实验中测量，即吸收或散射强度，通过结构数量（如原子位置或扭转角）与可观测数量（如平方结构因子幅度、NOE 强度或 (3)J 耦合常数）之间的理论推导关系。标准地用于将 (3)J 耦合与扭转角相关联的关系是 Karplus 关系，它既用于蛋白质结构精修，也用于评估蛋白质的模拟性质。使用三个不同蛋白质（Plastocyanin、Lysozyme 和 FKBP）的侧链结构和 (3)J（αβ）-耦合数据，研究了简单和广义 Karplus 关系的准确性，这些数据是可用的。结果表明，广泛使用的 Karplus 关系仅适用于蛋白质中 (3)J（αβ）-耦合与相应 χ(1)-角之间的关系的粗略估计。
