Lipopolysaccharide bilayer structure: effect of chemotype, core mutations, divalent cations, and temperature.
Lipopolysaccharide bilayer structure: effect of chemotype, core mutations, divalent cations, and temperature.
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DOI：
10.1021/bi990867d
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发表时间：
1999-07
期刊：
影响因子：
2.9
通讯作者：
S. Snyder;D. H. Kim;T. McIntosh
中科院分区：
文献类型：
--
作者：
S. Snyder;D. H. Kim;T. McIntosh
脂多糖（LPS）是革兰氏阴性菌表面的主要脂质，被认为是一种保护性和渗透性屏障。X-射线衍射分析的细菌应激的LPS多层膜被用来确定的结构和相互作用的性质的LPS从含有细菌生存所需的最小数量的糖（Re化学型）的菌株中发现的最大数量的糖粗糙的细菌（Ra化学型）。在20 ° C下，在不存在二价阳离子的情况下，LPS悬浮液在4.23 A处产生尖锐的广角反射，并且根据化学型在50-68 A处产生宽的低角带，表明存在由大的流体空间分隔的凝胶相双层。当施加渗透压时，并列的双层被挤压在一起，获得6 A分辨率的层状衍射。在较低的外加压力（<10（6）dyn/cm ~ 2）下，双层膜间的总排斥压力可用静电双电层理论解释。在较高的施加压力，有一个尖锐的向上突破，在每个压力-距离的关系，表明存在一个亲水性的立体屏障，其范围强烈依赖于LPS的化学型。这些向上断裂的位置，沿着电子密度分布，表明糖核宽度从Re化学型的10 A系统地增加到Ra化学型的27 A。在过量的缓冲液中，二价阳离子的加入使双层膜发生空间接触。电子密度分布用于确定阳离子结合位点和极性取代基的位置上的LPS寡糖核心。在液晶LPS双层中，每个烃链的面积约为26 A2，这表明酰基链堆积比在由典型膜脂质组成的双层中发现的要紧密得多。这种异常紧密的填充可能是LPS提供的渗透性屏障的关键因素。
Lipopolysaccharide (LPS), the primary lipid on the surface of Gram-negative bacteria, is thought to act as a protective and permeability barrier. X-ray diffraction analysis of osmotically stressed LPS multilayers was used to determine the structure and interactive properties of LPSs from strains containing the minimum number of sugars necessary for bacterial survival (Re chemotype) to the maximum number of sugars found in rough bacteria (Ra chemotype). At 20 degrees C in the absence of divalent cations, LPS suspensions gave a sharp wide-angle reflection at 4.23 A and a broad low-angle band centered at 50-68 A depending on the chemotype, indicating the presence of gel phase bilayers separated by large fluid spaces. As osmotic pressure was applied, the apposing bilayers were squeezed together and lamellar diffraction at 6 A resolution was obtained. At low applied pressures (<10(6) dyn/cm2), the total repulsive pressure between bilayers could be explained by electrostatic double layer theory. At higher applied pressures, there was a sharp upward break in each pressure-distance relation, indicating the presence of a hydrophilic steric barrier whose range depended strongly on the LPS chemotype. The positions of these upward breaks, along with electron density profiles, showed that the sugar core width systematically increased from 10 A for the Re chemotype to 27 A for the Ra chemotype. In excess buffer, the addition of divalent cations brought the bilayers into steric contact. Electron density profiles were used to determine the locations of cation binding sites and polar substituents on the LPS oligosaccharide core. The area per hydrocarbon chain was approximately 26 A2 in liquid-crystalline LPS bilayers, an indication of an acyl chain packing that is much tighter than that found in bilayers composed of typical membrane lipids. This unusually tight packing could be a critical factor in the permeability barrier provided by LPS.