Effects of Specific versus Nonspecific Ionic Interactions on the Structure and Lateral Organization of Lipopolysaccharides
Effects of Specific versus Nonspecific Ionic Interactions on the Structure and Lateral Organization of Lipopolysaccharides
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DOI：
10.1016/j.bpj.2011.03.019
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发表时间：
2011-05-04
影响因子：
3.4
通讯作者：
Winter, Roland
中科院分区：
文献类型：
--
作者：
Jeworrek, Christoph;Evers, Florian;Winter, Roland
我们报告的X射线反射率和掠入射X射线衍射测量脂多糖（LPS）单分子膜在水-空气界面。我们的研究表明，LPS分子的结构和横向排序是非常不同的磷脂系统，可以调制的离子强度的水亚相的离子依赖性的方式。我们的研究结果还表明，一价和二价离子的脂质结构域的二维排序的差异影响。Na+离子基于其有效屏蔽LPS分子的负电荷的能力而与LPS分子非特异性地相互作用，而Ca 2+离子通过交联单层中的相邻分子而特异性地相互作用。在低侧压下，Na+离子存在于亚相中导致LPS单层结构在大面积上有序，具有高压缩性，烃链的近六边形堆积，以及LPS头基区域的高密度。在较高的膜压力下，LPS单层变得更加刚性，导致LPS烃链的不太完美的倾斜堆积以及单层上高度有序的域的较小的横向尺寸。此外，与增加的表面压力相关联，糖头基的构象变化发生，导致整个LPS单层结构的增厚。亚相中的Ca 2+离子的作用是增加LPS单层的刚性，导致已经在低膜压下的烃链的倾斜堆积，糖部分的直立取向，以及单层平面中的有序域的小得多的尺寸。在亚相中同时存在Na+和Ca 2+离子的情况下，Na+的屏蔽效应在低膜压下占主导地位，而在较高的膜压下，LPS分子的结构和横向组织受Ca 2+离子的影响。非特异性的电荷屏蔽效应的Na+离子上的构象的糖部分变得不那么占主导地位，在生物相关的侧压力。
We report x-ray reflectivity and grazing incidence x-ray diffraction measurements of lipopolysaccharide (LPS) monolayers at the water-air interface. Our investigations reveal that the structure and lateral ordering of the LPS molecules is very different from phospholipid systems and can be modulated by the ionic strength of the aqueous subphase in an ion-dependent manner. Our findings also indicate differential effects of monovalent and divalent ions on the two-dimensional ordering of lipid domains. Na+ ions interact unspecifically with LPS molecules based on their ability to efficiently screen the negative charges of the LPS molecules, whereas Ca2+ ions interact specifically by cross-linking adjacent molecules in the monolayer. At low lateral pressures, Na+ ions present in the subphase lead to a LPS monolayer structure ordered over large areas with high compressibility, nearly hexagonal packing of the hydrocarbon chains, and high density in the LPS headgroup region. At higher film pressures, the LPS monolayer becomes more rigid and results in a less perfect, oblique packing of the LPS hydrocarbon chains as well as a smaller lateral size of highly ordered domains on the monolayer. Furthermore, associated with the increased surface pressure, a conformational change of the sugar headgroups occurs, leading to a thickening of the entire LPS monolayer structure. The effect of Ca2+ ions in the subphase is to increase the rigidity of the LPS monolayer, leading to an oblique packing of the hydrocarbon chains already at low film pressures, an upright orientation of the sugar moieties, and much smaller sizes of ordered domains in the plane of the monolayer. In the presence of both Na+- and Ca2+ ions in the subphase, the screening effect of Na+ is predominant at low film pressures, whereas, at higher film pressures, the structure and lateral organization of LPS molecules is governed by the influence of Ca2+ ions. The unspecific charge-screening effect of the Na+ ions on the conformation of the sugar moiety becomes less dominant at biologically relevant lateral pressures.