Teng Q, Nicholson L K, Cross T A
Department of Chemistry, Florida State University, Tallahassee 32306-3006.
J Mol Biol. 1991 Apr 5;218(3):607-19. doi: 10.1016/0022-2836(91)90705-b.
An analytical method for the determination of torsion angles from solid state 15N nuclear magnetic resonance (n.m.r.) spectroscopic data is demonstrated. Advantage is taken of the 15N-1H and 15N-13C dipolar interactions as well as the 15N chemical shift interaction in oriented samples. The membrane-bound channel conformation of gramicidin A has eluded an atomic resolution structure determination by more traditional approaches. Here, the torsion angles for the Ala3 site are determined by obtaining the n.m.r. data for both the Gly2-Ala3 and Ala3-Leu4 peptide linkages. Complete utilization of the orientational constraints derived from these orientation-dependent nuclear spin interactions in restricting the conformational space is most effectively achieved by utilizing spherical trigonometry. Two possible sets of torsion angles for the Ala3 site are obtained (phi, psi = -129 degrees, 153 degrees and -129 degrees, 122 degrees), both of which are consistent with a right-handed beta-helix. Other functional and computational evidence strongly supports the set for which the carbonyl oxygen atom of the Ala3-Leu4 linkage is rotated into the channel lumen.
本文展示了一种从固态15N核磁共振（n.m.r.）光谱数据中确定扭转角的分析方法。该方法利用了取向样品中的15N-1H和15N-13C偶极相互作用以及15N化学位移相互作用。短杆菌肽A的膜结合通道构象一直未能通过更传统的方法确定其原子分辨率结构。在此，通过获取Gly2-Ala3和Ala3-Leu4肽键的n.m.r.数据来确定Ala3位点的扭转角。通过利用球面三角学，最有效地实现了完全利用这些依赖于取向的核自旋相互作用所产生的取向约束来限制构象空间。获得了Ala3位点的两组可能的扭转角（φ，ψ = -129°，153°和 -129°，122°），这两组都与右手β-螺旋一致。其他功能和计算证据有力地支持了Ala3-Leu4键的羰基氧原子旋转到通道腔内的那一组。
