Seydel U, Koch M H, Brandenburg K
Forschungsinstitut Borstel, Germany.
J Struct Biol. 1993 May-Jun;110(3):232-43. doi: 10.1006/jsbi.1993.1026.
The structural polymorphisms of rough mutant lipopolysaccharides (LPS) Rd, Rc, Rb, and Ra from Salmonella minnesota (strains R4, R7, Rz, R5, R345, and R60, respectively) were investigated as a function of temperature, water content, and Mg2+ concentration. The gel to liquid crystalline (beta<==>alpha) phase transition temperature (Tc) and the state of order within each phase were measured by Fourier transform infrared spectroscopy. The amount of bound water was determined by differential scanning calorimetry and the three-dimensional structures in each phase state were characterized by synchrotron radiation X-ray diffraction. The results indicate an extremely complex dependence of the structural behavior of LPS on ambient conditions. The beta<==>alpha acyl chain melting temperatures at high water contents (95-97%), Tc = 31 to 32 degrees C for LPS Rd, 33 to 35 degrees C for LPS Rc to Rb, and 36 degrees C for LPS Ra, increase with decreasing water content and in the presence of Mg2+ cations with a concomitant broadening of the transition range. Below 30 to 50% water content, no distinct phase transitions can be observed. These effects are most pronounced for LPS with the shortest sugar chains. Below 50% water content, only lamellar structures can be observed in the temperature range 5 to 80 degrees C, independent of the Mg2+ concentration. Above 50% water concentration, for large [LPS]:[Mg2+] molar ratios the predominant structure above Tc is nonlamellar; for smaller [LPS]:[Mg2+] molar ratios a superposition of lamellar and nonlamellar structures is found. For all LPS Rd to Rb at low Mg2+ concentrations, the phase transition is connected with a change in the three-dimensional structure from lamellar or mixed lamellar/nonlamellar to a pure nonlamellar, probably cubic structure. The tendency to form non-lamellar structures decreases with the length of the core oligosaccharide. At an equimolar ratio of [LPS] and [Mg2+] a multibilayered organization is observed. Some of the nonlamellar structures are cubic phases with periodicities between 12 and 16 nm. The molecular dimensions of the single endotoxin molecules in the absence and the presence of external water are estimated from the different lamellar periodicities, including those of free lipid A and deep rough mutant LPS Re. These observations are discussed with respect to the biological importance of LPS as a potent inducer of biological effects in mammals.
对来自明尼苏达沙门氏菌（分别为菌株R4、R7、Rz、R5、R345和R60）的粗糙突变型脂多糖（LPS）Rd、Rc、Rb和Ra的结构多态性，作为温度、含水量和Mg2 +浓度的函数进行了研究。通过傅里叶变换红外光谱法测量凝胶到液晶（β⇔α）的相变温度（Tc）以及每个相内的有序状态。通过差示扫描量热法测定结合水的量，并通过同步辐射X射线衍射表征每个相态的三维结构。结果表明LPS的结构行为对环境条件有着极其复杂的依赖性。在高含水量（95 - 97%）时，β⇔α酰基链的熔化温度，LPS Rd为Tc = 31至32℃，LPS Rc至Rb为33至35℃，LPS Ra为36℃，随着含水量的降低以及在Mg2 +阳离子存在的情况下，转变范围会变宽，熔化温度升高。在含水量低于30%至50%时，无法观察到明显的相变。这些效应对于糖链最短的LPS最为明显。在含水量低于50%时，在5至80℃的温度范围内仅能观察到层状结构，与Mg2 +浓度无关。在含水量高于50%时，对于大的[LPS]：[Mg2 +]摩尔比，高于Tc时的主要结构是非层状的；对于较小的[LPS]：[Mg2 +]摩尔比，则发现层状和非层状结构的叠加。对于所有低Mg2 +浓度下的LPS Rd至Rb，相变与三维结构从层状或混合层状/非层状变为纯非层状（可能是立方结构）的变化相关。形成非层状结构的趋势随着核心寡糖长度的增加而降低。在[LPS]和[Mg2 +]等摩尔比时，观察到多层组织。一些非层状结构是周期在12至16nm之间的立方相。根据不同的层状周期，包括游离脂质A和深度粗糙突变型LPS Re的层状周期，估算了在有无外部水存在时单个内毒素分子的分子尺寸。针对LPS作为哺乳动物生物效应的有效诱导剂的生物学重要性，对这些观察结果进行了讨论。
