Effect of chain length and unsaturation on elasticity of lipid bilayers
Effect of chain length and unsaturation on elasticity of lipid bilayers
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DOI：
10.1016/s0006-3495(00)76295-3
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发表时间：
2000-07-01
影响因子：
3.4
通讯作者：
Evans, E
中科院分区：
文献类型：
--
作者：
Rawicz, W;Olbrich, KC;Evans, E
用微管加压法测定了磷脂酰胆碱（PC）膜的弹性弯曲系数k（c）和面积拉伸系数K-A。选择12种二酰基PC：八个具有两个18碳链并且每个脂质的不饱和度从一个双键（C18：1/0，C18：0/1）到六个双键（diC 18：3），两个具有短的饱和碳链（diC 13：0，diC 14：0），并且两个具有长的不饱和碳链（diC 20：4，diC 22：1）。弯曲模量来自于在非常低的张力（0.001- 0.5mN/m）下囊泡表面积中的表观膨胀的测量，所述张力由热弯曲波动的平滑化主导。面积拉伸模量是从高张力（>0.5 mN/m）下囊泡表面膨胀的测量中获得的，这涉及到每个分子面积的增加和残余热波动的平滑化的小但重要的贡献。直接拉伸模量随链不饱和度或长度变化很小（< +10%），平均约为243 mN/m。另一方面，饱和/单不饱和链PC的弯曲模量随着链长从diC 13：0的0.56 x 10（-19）J逐渐增加到diC 22：1的1.2 x 10（-19）J。然而，对于较长的链，当链中存在两个或更多个顺式双键（C18：0/2、diC 18：2、diC 18：3、diC 20：4）时，弯曲模量非常出乎意料地急剧下降至接近0.4 × 10（-19）J。鉴于面积拉伸模量几乎恒定，弯曲刚度随链长和多不饱和度的变化意味着厚度的显着变化。为了检验这一假设，峰-峰的头基厚度h（PP）的双层从x-射线衍射的multibilayer阵列在受控的相对湿度。对于饱和/单不饱和链双层，如预期的，距离h（pp）从diC 13：0平滑地增加到diC 22：1。此外，该距离和弹性性质与双层的聚合物刷模型良好地相关，该模型规定弹性比（k（c）/K-A）（1/2）=（h（pp）- h（o））/24，其中h（o）近似于1 nm说明头基峰与可变形烃区域的分离。然而，diC 18：2、diC 18：3和diC 20：4的弹性比和厚度落入低于相关性的不同组中，这表明多顺式不饱和链双层比饱和/单不饱和链双层更薄且更柔性。
Micropipette pressurization of giant bilayer vesicles was used to measure both elastic bending k(c), and area stretch K-A moduli of fluid-phase phosphatidylcholine (PC) membranes. Twelve diacyl PCs were chosen: eight with two 18 carbon chains and degrees of unsaturation from one double bond (C18:1/0, C18:0/1) to six double bonds per lipid (diC18:3), two with short saturated carbon chains (diC13:0, diC14:0), and two with long unsaturated carbon chains (diC20:4, diC22:1). Bending moduli were derived from measurements of apparent expansion in vesicle surface area under very low tensions (0.001-0.5 mN/m), which is dominated by smoothing of thermal bending undulations. Area stretch moduli were obtained from measurements of vesicle surface expansion under high tensions (>0.5 mN/m), which involve an increase in area per molecule and a small-but important-contribution from smoothing of residual thermal undulations. The direct stretch moduli varied little (< +10%) with either chain unsaturation or length about a mean of 243 mN/m. On the other hand, the bending moduli of saturated/monounsaturated chain PCs increased progressively with chain length from 0.56 x 10(-19) J for diC13:0 to 1.2 x 10(-19) J for diC22:1. However, quite unexpectedly for longer chains, the bending moduli dropped precipitously to similar to 0.4 x 10(-19) J when two or more cis double bonds were present in a chain (C18:0/2, diC18:2, diC18:3, diC20:4). Given nearly constant area stretch moduli, the variations in bending rigidity with chain length and polyunsaturation implied significant variations in thickness. To test this hypothesis, peak-to-peak headgroup thicknesses h(pp) of bilayers were obtained from x-ray diffraction of multibilayer arrays at controlled relative humidities. For saturated/monounsaturated chain bilayers, the distances h(pp) increased smoothly from diC13:0 to diC22:1 as expected. Moreover, the distances and elastic properties correlated well with a polymer brush model of the bilayer that specifies that the elastic ratio (k(c)/K-A)(1/2) = (h(pp) - h(o))/24, where h(o) approximate to 1 nm accounts for separation of the headgroup peaks from the deformable hydrocarbon region. However, the elastic ratios and thicknesses for diC18:2, diC18:3, and diC20:4 fell into a distinct group below the correlation, which showed that poly-cis unsaturated chain bilayers are thinner and more flexible than saturated/monounsaturated chain bilayers.