Cherchi G M, Formato M, Demuro P, Masserini M, Varani I, DeLuca G
Institute of Applied Biology, University of Sassari, Italy.
Biochim Biophys Acta. 1994 Jun 2;1212(3):345-52. doi: 10.1016/0005-2760(94)90209-7.
Glycosaminoglycan (GAG)-protein complexes from human plasma were separated into low charge (LC-GP) and high charge (HC-GP) components. LC-GP and HC-GP differed with respect to GAG and protein composition and to molecular size. The in vitro interaction of both GAG-protein complexes with human LDL was investigated. LC-GP did not precipitate LDL. On the contrary, HC-GP formed insoluble complexes with LDL, following a biphasic behaviour on increasing HC-GP concentration. In the presence of a HC-GP/LDL ratio higher than 0.02 the interaction stoichiometry was shifted towards the formation of soluble complexes. Papain treatment of HC-GP completely prevented LDL precipitation. Moreover, the extent of HC-GP-induced precipitation of LDL was markedly reduced by the simultaneous addition of LC-GP. Data obtained with standard GAGs showed that heparin (HE) and chondroitin-6-sulphate (C6S) were the most effective ligands in precipitating LDL. However, the shape of precipitation curves was markedly different. C6S behaved similarly to HC-GP, suggesting that GAG chains could play an important role in insoluble complex formation with LDL. Steady-state fluorescence anisotropy investigation indicated that HC-GP induced a significant decrease in the microviscosity of LDL hydrophobic region. This effect was no longer detectable after either addition of LC-GP or papain treatment of HC-GP. Differential scanning calorimetry (DSC) demonstrated that both lipid and protein components of LDL were affected by the interaction with HC-GP. The temperature of irreversible thermal unfolding of apo B100 was shifted to a lower value and a second peak appeared in the region of the reversible melting of cholesterol esters. Both the fluorescence anisotropy and the DSC data obtained with standard HE and C6S indicated that GAG chains were directly involved in affecting physico-chemical properties of complexed LDL. These results suggest that the interaction with plasma HC-GP could modify LDL structural properties. However, LC-GP is likely to act as a modulator, probably preventing the interaction between HC-GP and circulating LDL.
从人血浆中分离出的糖胺聚糖（GAG）-蛋白质复合物被分为低电荷（LC-GP）和高电荷（HC-GP）组分。LC-GP和HC-GP在GAG和蛋白质组成以及分子大小方面存在差异。研究了这两种GAG-蛋白质复合物与人低密度脂蛋白（LDL）的体外相互作用。LC-GP不会使LDL沉淀。相反，HC-GP与LDL形成不溶性复合物，随着HC-GP浓度的增加呈现双相行为。当HC-GP/LDL比率高于0.02时，相互作用化学计量向可溶性复合物的形成转变。木瓜蛋白酶处理HC-GP可完全阻止LDL沉淀。此外，同时添加LC-GP可显著降低HC-GP诱导的LDL沉淀程度。使用标准GAG获得的数据表明，肝素（HE）和硫酸软骨素-6-硫酸盐（C6S）是沉淀LDL最有效的配体。然而，沉淀曲线的形状明显不同。C6S的行为与HC-GP相似，表明GAG链在与LDL形成不溶性复合物中可能起重要作用。稳态荧光各向异性研究表明，HC-GP导致LDL疏水区域的微粘度显著降低。添加LC-GP或对HC-GP进行木瓜蛋白酶处理后，这种效应不再可检测到。差示扫描量热法（DSC）表明，LDL的脂质和蛋白质成分均受到与HC-GP相互作用的影响。载脂蛋白B100不可逆热解折叠的温度向较低值移动，并且在胆固醇酯可逆熔化区域出现第二个峰。使用标准HE和C6S获得的荧光各向异性和DSC数据均表明，GAG链直接参与影响复合LDL的物理化学性质。这些结果表明，与血浆HC-GP的相互作用可能会改变LDL的结构性质。然而，LC-GP可能起到调节剂的作用，可能会阻止HC-GP与循环LDL之间的相互作用。
