Conformational response of the phosphatidylcholine headgroup to bilayer surface charge: torsion angle constraints from dipolar and quadrupolar couplings in bicelles
Conformational response of the phosphatidylcholine headgroup to bilayer surface charge: torsion angle constraints from dipolar and quadrupolar couplings in bicelles
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DOI：
10.1002/mrc.1333
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发表时间：
2004-02-01
影响因子：
2
通讯作者：
Macdonald, PM
中科院分区：
文献类型：
--
作者：
Semchyschyn, DJ;Macdonald, PM
利用分别在1 - 棕榈酰 - 2 - 油酰 - sn - 甘油 - 3 - 磷酸胆碱（POPC）的磷酸胆碱基团用氘（POPC - α - d₂、POPC - β - d₂和POPC - γ - d₉）或碳 - 13（POPC - α - C - 13和POPC - αβ - C - 13₂）标记的H - 2和C - 13核磁共振谱中的四极分裂和偶极分裂的扭转角分析，研究了双层表面电荷对磷脂酰胆碱的磷酸胆碱基团构象的影响。将其掺入含有不同量的阳离子两亲物1,2 - 二肉豆蔻酰 - 3 - 三甲铵丙烷（DMTAP）或阴离子两亲物1,2 - 二肉豆蔻酰 - sn - 甘油 - 3 - 磷酸甘油（DMPG）的磁性排列的双分子层中。在每种表面电荷下，测量了三组四极分裂（分别来自三个氘标记位置中的每一个）和三组偶极分裂（C - 13(α) - P - 31、C - 13(α) - C - 13(β)、C - 13(β) - N - 14）以及P - 31剩余化学位移各向异性。扭转角分析假定POPC围绕其长分子轴快速各向异性旋转，从而将所有核磁共振相互作用投影到该运动的指向轴上。通过首先在围绕指向轴进行运动平均之前转换到固定在磷酸胆碱基团上的公共参考系，计算偶极、四极和化学位移各向异性作为磷酸胆碱内部扭转角的函数。实验和计算的比较提供了两个指定指向相对于分子取向的序参数，以及扭转角α₃、α₄和α₅。发现表面电荷对扭转角α₅（围绕C - α - C - β的旋转）影响很小，但对扭转角α₃[围绕P - O(11)的旋转]和α₄[围绕O(11) - C - α的旋转]有较大且相反的影响，相对于中性情况，在阳离子表面电荷存在时，P - N向量产生净向上倾斜，在阴离子表面电荷存在时产生向下倾斜。版权所有（C）2004约翰威立父子有限公司
The effects of bilayer surface charge on the conformation of the phosphocholine group of phosphatidylcholine were investigated using a torsion angle analysis of quadrupolar and dipolar splittings in, respectively, H-2 and C-13 NMR spectra of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) labelled in the phosphocholine group with either deuterons (POPC-alpha-d(2), POPC-beta-d(2) and POPC-gamma-d(9)) or carbon-13 (POPC-alpha-C-13 and POPC-alphabeta-C-13(2)) and incorporated into magnetically aligned bicelles containing various amounts of either the cationic amphiphile 1,2-dimyristoyl-3-trimethylammoniumpropane (DMTAP) or the anionic amphiphile 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG). Three sets of quadrupolar splittings, one from each of the three deuteron labelling positions, and three sets of dipolar splittings (C-13(alpha)-P-31, C-13(alpha)-C-13(beta), C-13(beta)-N-14), were measured at each surface charge, along with the P-31 residual chemical shift anisotropy. The torsion angle analysis assumed fast anisotropic rotation of POPC about its long molecular axis, thus projecting all NMR interactions onto that director axis of motion. Dipolar, quadrupolar and chemical shift anisotropies were calculated as a function of the phosphocholine internal torsion angles by first transforming into a common reference frame affixed to the phosphocholine group prior to motional averaging about the director axis. A comparison of experiment and calculation provided the two order parameters specifying the director orientation relative to the molecule, plus the torsion angles alpha(3), alpha(4) and alpha(5). Surface charge was found to have little effect on the torsion angle alpha(5) (rotations about C-alpha-C-beta), but to have large and inverse effects on torsion angles alpha(3) [rotations about P-O(11)] and alpha(4) [rotations about O(11)-C-alpha], yielding a net upwards tilt of the P-N vector in the presence of cationic surface charge, and a downwards tilt in the presence of anionic surface charge, relative to neutrality. Copyright (C) 2004 John Wiley Sons, Ltd.