Conformational constraints on the headgroup and sn-2 chain of bilayer DMPC from NMR dipolar couplings
Conformational constraints on the headgroup and sn-2 chain of bilayer DMPC from NMR dipolar couplings
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DOI：
10.1021/bi953083i
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发表时间：
1996-06-25
期刊：
影响因子：
2.9
通讯作者：
Zimmermann, H
中科院分区：
文献类型：
--
作者：
Hong, M;Schmidt-Rohr, K;Zimmermann, H
本文给出了液晶双层膜中1，2-dimyristoyl-m-glycero-3-phosphatidylcholine(二甲基丙三醇)的头基、甘油主链和sn-2链构象的新的核磁共振约束。利用二维C-13-H-1化学位移相关谱，我们发现了羧基碳二氧化碳和头基质子之间存在显著的偶极耦合。这表明DMPC头基和SN-2链的开始相互弯曲的构象在流体双层中被显著填充。文献中的P-31-C-13偶极耦合进一步证实了这种头基取向的优势，这种偶极耦合限制了甘油G2-G3的扭转角接近TRAN，排除了在DMPC晶体中发现的两种构象中的一种。结合和重新考察了已知的20个甘油主链及其相邻链段的核磁共振偶联，我们发现DMPC分子核心的几个扭转角度和键方向受到严重的限制，肯定与晶体结构上的不同。我们提出了一个一致的液晶相磷胆碱脂的分子模型，在分子的核心有一个刚性的主链，一个弯曲的头基，并增加了向酰链末端和头基的迁移率。
This paper presents new NMR constraints on the conformation of the headgroup, glycerol backbone, and sn-2 chain of 1,2-dimyristoyl-m-glycero-3-phosphatidylcholine (DMPC) in the liquid-crystalline bilayer. Using two-dimensional C-13-H-1 chemical shift correlation spectroscopy, we find significant dipolar couplings between the carboxyl carbon CO2 and the headgroup protons. This indicates that a conformation in which the DMPC headgroup and the beginning of the sn-2 chain bend toward each other is significantly populated in the fluid bilayer. The predominance of this headgroup orientation can be further confirmed by P-31-C-13 dipolar couplings from the literature, which constrain the glycerol G2-G3 torsion angle to be close to trans, excluding a significant presence of one of the two conformations found in the DMPC crystal. Combining and reexamining 20 known NMR couplings for the glycerol backbone and its adjacent segments of L(alpha)-DMPC, we find that several torsion angles and bond orientations in the core of the DMPC molecule are constrained severely and must differ from those in the crystal structure. We propose a consistent molecular model for phosphocholine lipids in the liquid-crystalline phase, with a rigid backbone in the core of the molecule, a bent-back headgroup, and increasing mobility toward the ends of the acyl chains and the headgroup.