Suntory Foundation for Life Sciences, Bioorganic Research Institute, Mishima-Gun, Osaka, Japan.
J Phys Chem B. 2011 Dec 22;115(50):14991-5001. doi: 10.1021/jp208958a. Epub 2011 Nov 30.
Inhomogeneous line broadening due to conformational distributions of molecules is one of the troublesome problems in solid-state NMR spectroscopy. The best possible way to avoid it is to crystallize the sample. Here, we present a highly resolved (13)C cross-polarization (CP) magic angle spinning (MAS) NMR spectrum of the highly ordered crystalline 1,2-dimyrystoyl-sn-glycero-3-phosphocholine (DMPC) and completely assigned it using two-dimensional (2D) solid-state NMR spectra, dipolar heteronuclear correlation (HETCOR) spectra, scalar heteronuclear J coupling based chemical shift correlation (MAS-J-HMQC) spectra, and Dipolar Assisted Rotational Resonance (DARR) spectra. A comparison between assigned chemical shift values by solid-state NMR in this study and the calculated chemical shift values for X-ray crystal DMPC structures shows good agreement, indicating that the two isomers in the crystalline DMPC take the same conformation as the X-ray crystal structure. The phase diagram of the low hydration level of DMPC (3 ≤ n(W) ≤ 12) determined by (1)H and (13)C NMR spectra indicates that DMPC takes a crystalline state only in a very narrow region around n(W) = 4 and T < 313 K. These findings provide us with conformational information on crystalline DMPC and the physical properties of DMPC at a low hydration level and can possibly help us obtain a highly resolved solid-state NMR spectrum of microcrystalline membrane-associated protein samples.
由于分子构象分布导致的不均匀线宽是固态 NMR 光谱学中的一个难题。避免这个问题的最好方法是结晶样品。在这里,我们呈现了高度有序的结晶 1,2-二肉豆蔻酰-sn-甘油-3-磷酸胆碱(DMPC)的高分辨率(13)C 交叉极化(CP)魔角旋转(MAS)NMR 谱,并使用二维(2D)固态 NMR 谱、偶极异核相关(HETCOR)谱、基于标量异核 J 偶合的化学位移相关(MAS-J-HMQC)谱和偶极辅助旋转共振(DARR)谱对其进行了完全归属。本研究中通过固态 NMR 归属的化学位移值与 X 射线晶体 DMPC 结构的计算化学位移值进行比较,结果表明两者吻合较好,表明结晶 DMPC 中的两种异构体与 X 射线晶体结构具有相同的构象。通过(1)H 和(13)C NMR 谱确定的低水合水平(3≤n(W)≤12)的 DMPC 相图表明,DMPC 仅在 n(W)=4 左右和 T<313 K 的非常窄的区域内呈结晶态。这些发现为我们提供了结晶 DMPC 的构象信息和低水合水平下 DMPC 的物理性质,可能有助于我们获得微晶膜相关蛋白样品的高分辨率固态 NMR 谱。