Lateral lipid diffusion dominates NOESY cross-relaxation in membranes
Lateral lipid diffusion dominates NOESY cross-relaxation in membranes
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DOI：
10.1021/ja9944756
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发表时间：
2000-04-26
影响因子：
15
通讯作者：
Gawrisch, K
中科院分区：
文献类型：
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作者：
Yau, WM;Gawrisch, K
最近，我们将液晶磷脂双层中实验确定的 NOESY 交叉弛豫速率与通过 10 ns 分子动力学 (MD) 模拟计算的理论值进行了比较。 MD 模拟提供了自相关函数，因此提供了膜中磁偶极子-偶极子相互作用的谱密度函数。相关函数因脂质运动而衰减，包括键振动、烃链和头基的左/反式异构化、整个脂质的分子旋转和摆动以及脂质分子的横向扩散。 1 我们计算了不同运动的强度因子和相关时间，以量化它们对相关函数的贡献。分析明确表明，相关时间显着超过模拟长度的运动对交叉弛豫的贡献最大。假设最慢运动 1 sa 值的相关时间为 170 ns，这表明横向脂质扩散，获得了极好的一致性。 2 在这篇文章中，我们提供了实验证据，证明横向扩散速率确实是脂膜交叉弛豫速率的通用比例因子。首先，让我们解释横向扩散如何影响交叉松弛。交叉弛豫率 Γij 取决于谱密度 Jij (ω)，其中 ω0 是质子拉莫尔频率，是结合常数的因子。由于环境温度下所有测得的交叉弛豫率均为负值，因此我们得出结论，零频率下的谱密度 Jij (0) 占主导地位。脂质双层中的谱密度函数可以通过与上面列出的各种运动相关的项之和来近似，其中 τn 是相关时间和相应的强度因子。 1 零频率处的频谱密度与 anτn 乘积之和成正比。具有最长相关时间的运动的典型强度约为总强度的百分之五。 1 尽管振幅较小，但相应的相关时间 τn) 170 ns 的较大值使得最慢的运动（可能是横向扩散）成为对谱密度的主要贡献。因此，所有脂质交叉弛豫速率都预计与单个相关时间成比例，该相关时间取决于横向扩散速率，并且与横向扩散具有相同的温度依赖性。这一预测经过了实验检验。
Recently, we compared experimentally determined rates of NOESY cross-relaxation in liquid-crystalline phospholipid bilayers with theoretical values calculated from a 10 ns molecular dynamics (MD) simulation. The MD simulation provided autocorrelation functions, and consequently, spectral density functions of magnetic dipole-dipole interactions in a membrane. Correlation functions decayed as a result of lipid motion, including bond vibrations, gauche/trans isomerization of hydrocarbon chains and headgroups, molecular rotation and wobble of the entire lipid, and lateral diffusion of lipid molecules. 1 We calculated intensity factors and correlation times for the different motions to quantitate their contribution to the correlation functions. The analysis showed unambiguously that motions with correlation times that significantly exceeded the length of the simulation made the largest contribution to cross-relaxation. Excellent agreement was achieved, assuming a correlation time of 170 ns for the slowest motion1 sa value that is suggestive for lateral lipid diffusion. 2 In this contribution, we provide experimental evidence that the rate of lateral diffusion is indeed a universal scaling factor for rates of cross-relaxation in lipid membranes. First, let us explain how lateral diffusion influences crossrelaxation. The cross-relaxation rates, Γij, depend on the spectral densities Jij (ω) where ω0 is the proton Larmor frequency and is a factor that combines the constants. Because all measured cross-relaxation rates at ambient temperature are negative, we concluded that the spectral densities at zero frequency, Jij (0), are dominant. The spectral density functions in lipid bilayers can be approximated by a sum of terms that are linked to the various motions listed above where τn are correlation times and an the corresponding intensity factors. 1 Spectral density at frequency zero is proportional to the sum of products anτn. Typical intensities of the motions with the longest correlation time are of the order of five percent of total intensity. 1 Despite their small amplitude, the large value of the corresponding correlation time, τn) 170 ns, makes the slowest motion, presumably lateral diffusion, the dominant contribution to spectral density. Consequently, all rates of lipid cross-relaxation are predicted to scale with a single correlation time that depends on the rate of lateral diffusion and has the same temperature dependence as lateral diffusion. This prediction was tested experimentally.