Jürgens G, Müller M, Koch M H, Brandenburg K
Forschungszentrum Borstel, Division of Biophysics, D-23845 Borstel, Germany.
Eur J Biochem. 2001 Aug;268(15):4233-42. doi: 10.1046/j.1432-1327.2001.02338.x.
The interaction of hemoglobin (Hb) with endotoxins [i.e. with enterobacterial deep rough mutant lipopolysaccharide (LPS) Re and the "endotoxic principle" of LPS, lipid A] was investigated using a variety of physical techniques and with two biological assays, tumor necrosis factor (TNF)-alpha induction in human mononuclear cells and the Limulus amebocyte lysate (LAL) assay. Fourier-transform IR-spectroscopic experiments indicate nonelectrostatic binding to the hydrophobic moiety with a slight rigidification of the lipid A acyl chains, and an increase in the inclination of the lipid A backbone with respect to the membrane surface from 35 degrees to more than 40 degrees due to Hb binding, but no change of the predominantly alpha-helical secondary structures of Hb due to LPS binding. From isothermal titration calorimetry, the molar [Hb] : [endotoxin] binding ratio lies between 1 : 3 and 1 : 5 molar. Synchrotron radiation X-ray diffraction measurements indicate a reorientation of the lipid A aggregates from one cubic structure to another, the final structure belonging to space group Q224. The LPS-induced TNF-alpha production of mononuclear cells is enhanced by Hb, whereas in the LAL assay an LPS concentration-dependent increase or decrease was observed. Although a detailed mechanism of action cannot be given, the enhancement of LPS bioactivity can be understood in the light of the previously presented conformational concept; Hb induces an increase in the conical shape of the lipid A moiety of LPS, higher cross-section of the hydrophobic than the hydrophilic part, and of the inclination angle of the diglucosamine backbone with respect to the direction of the acyl chains.
利用多种物理技术以及两种生物学检测方法，即人单核细胞中肿瘤坏死因子（TNF）-α诱导实验和鲎试剂检测法，研究了血红蛋白（Hb）与内毒素[即与肠杆菌深粗糙突变型脂多糖（LPS）Re以及LPS的“内毒素核心成分”脂质A]之间的相互作用。傅里叶变换红外光谱实验表明，Hb与脂质A的疏水部分存在非静电结合，脂质A酰基链略有刚性化，并且由于Hb结合，脂质A主链相对于膜表面的倾斜角度从35度增加到40度以上，但LPS结合并未导致Hb主要的α-螺旋二级结构发生变化。等温滴定量热法结果显示，[Hb]：[内毒素]的摩尔结合比在1：3至1：5摩尔之间。同步辐射X射线衍射测量表明，脂质A聚集体从一种立方结构重新定向为另一种立方结构，最终结构属于空间群Q224。Hb可增强LPS诱导的单核细胞TNF-α产生，而在鲎试剂检测法中，观察到LPS浓度依赖性的增加或减少。尽管无法给出详细的作用机制，但根据之前提出的构象概念，可以理解LPS生物活性的增强；Hb导致LPS脂质A部分的锥形形状增加，疏水部分比亲水部分具有更大的横截面，以及二葡糖胺主链相对于酰基链方向的倾斜角度增加。
