Rotation of lipids in membranes:: Molecular dynamics simulation, 31P spin-lattice relaxation, and rigid-body dynamics
Rotation of lipids in membranes:: Molecular dynamics simulation, 31P spin-lattice relaxation, and rigid-body dynamics
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DOI：
10.1529/biophysj.107.121806
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发表时间：
2008-04-15
影响因子：
3.4
通讯作者：
Pastor, Richard W.
中科院分区：
文献类型：
--
作者：
Klauda, Jeffery B.;Roberts, Mary F.;Pastor, Richard W.
分子动力学模拟和P-31-NMR自旋晶格（R-1）弛豫速率从0.022至21.1 T的流体相二棕榈酰磷脂酰胆碱双层进行了比较。实验和模拟直接预测之间的协议表明，占主导地位的缓慢弛豫（相关）时间的偶极和化学位移各向异性自旋晶格弛豫分别为10 ns和3 ns。整体重新定位的脂质体，由磷，甘油，anclacyl链，是很好地描述了一个刚体模型。摆动，垂直于D = 1-2 × 10（8）s（-1），是10 ns弛豫的主要成分;该时间尺度与液体十六烷粘度介质中脂质大小的圆柱体的翻滚一致。由于通过快速运动和摆动求平均值，因此很难精确确定平行于的D值，即绕脂质体长轴旋转的扩散常数;初步估计为1 × 10（7）s（-1）。得到的D-平行/D-垂直近似为0。1意味着轴向旋转强烈调制的脂质/水界面处的相互作用。刚体建模和潜在的平均力评价表明，胆碱组是相对解耦的其余脂质。这是一致的化学位移各向异性和偶极相关时间的比例，这里报道和以前的观察，P-31-NMR lineeshapes轴对称，即使在凝胶相的二棕榈酰磷脂酰胆碱。
Molecular dynamics simulations and P-31-NMR spin-lattice (R-1) relaxation rates from 0.022 to 21.1 T of fluid phase dipalmitoylphosphatidylcholine bilayers are compared. Agreement between experiment and direct prediction from simulation indicates that the dominant slow relaxation (correlation) times of the dipolar and chemical shift anisotropy spin-lattice relaxation are similar to 10 ns and 3 ns, respectively. Overall reorientation of the lipid body, consisting of the phosphorus, glycerol, anclacyl chains, is well described within a rigid-body model. Wobble, with D-perpendicular to = 1-2 X 10(8) s(-1), is the primary component of the 10 ns relaxation; this timescale is consistent with the tumbling of a lipid-sized cylinder in a medium with the viscosity of liquid hexadecane. The value for D parallel to, the diffusion constant for rotation about the long axis of the lipid body, is difficult to determine precisely because of averaging by fast motions and wobble; it is tentatively estimated to be 1 X 10(7)s(-1). The resulting D-parallel to/D-perpendicular to approximate to 0. 1 implies that axial rotation is strongly modulated by interactions at the lipid/water interface. Rigid-body modeling and potential of mean force evaluations show that the choline group is relatively uncoupled from the rest of the lipid. This is consistent with the ratio of chemical shift anisotropy and dipolar correlation times reported here and the previous observations that P-31-NMR lineshapes are axially symmetric even in the gel phase of dipalmitoylphosphatidylcholine.