Walsh M T, Atkinson D
J Lipid Res. 1986 Mar;27(3):316-25.
Apoprotein B, the major apoprotein of normal human low density lipoprotein (LDL) was solubilized with sodium deoxycholate (NaDC). The protein was recombined with the phospholipid dimyristoyl phosphatidylcholine (DMPC) to produce a complex of DMPC-apoB (4:1 w/w). (Biochemistry. 22: 3170-3178. 1983). Carboxyfluorescein and [3H]dextran entrapment studies show the DMPC-apoB 4:1 (w/w) complex to encapsulate an aqueous volume of 0.17 microliter/mumol of DMPC. From the chemistry and morphology of the complex and the evidence that the complex possesses an encapsulated volume, the most appropriate structural model for this assembly is that of a phospholipid single bilayer vesicle into which apoB is incorporated. Differential scanning calorimetry (DSC) and circular dichroic spectroscopy (CD) were used to investigate the physical properties of apoB in the mixed micellar complex with NaDC and in the vesicular DMPC-apoB complex. CD studies of apoB in NaDC mixed micelles show that apoB exhibits a similar secondary structure as apoB of native LDL over the temperature range 5-30 degrees C. Reversible structural changes occur between 30 and 50 degrees C. However, above 50 degrees C, disruption of the micellar particle and endothermic protein unfolding and denaturation occur with a Tmax of 52 degrees C and an enthalpy of 0.22 cal/g apoB, as shown by DSC. The DMPC-apoB complex exhibits a reversible thermal transition centered at 24 degrees C (delta H = 3.34 Kcal/mol DMPC) which is associated with the order-disorder transition of the hydrocarbon chains of DMPC. An endothermic transition occurs over the range 53-70 degrees C (delta H = 2.09 cal/g apoB) which, as shown by CD and turbidity study, corresponds to protein unfolding-denaturation and particle disruption. CD shows that apoB in the vesicular environment undergoes a series of conformational changes. The major alterations occur over the temperature range of the order-disorder transition of the phospholipid. Between 37-60 degrees C, the conformation is similar to that observed in native LDL.
载脂蛋白B，即正常人低密度脂蛋白（LDL）的主要载脂蛋白，用脱氧胆酸钠（NaDC）进行增溶。将该蛋白质与磷脂二肉豆蔻酰磷脂酰胆碱（DMPC）重新组合，以产生DMPC - 载脂蛋白B复合物（4:1 w/w）。（《生物化学》。22: 3170 - 3178。1983年）。羧基荧光素和[3H]葡聚糖包封研究表明，DMPC - 载脂蛋白B 4:1（w/w）复合物每微摩尔DMPC包封0.17微升的水相体积。从复合物的化学性质和形态以及复合物具有包封体积的证据来看，该组装体最合适的结构模型是载脂蛋白B掺入其中的磷脂单分子层囊泡。差示扫描量热法（DSC）和圆二色光谱法（CD）用于研究载脂蛋白B在与NaDC形成的混合胶束复合物以及囊泡状DMPC - 载脂蛋白B复合物中的物理性质。对载脂蛋白B在NaDC混合胶束中的CD研究表明，在5 - 30℃的温度范围内，载脂蛋白B呈现出与天然LDL的载脂蛋白B相似的二级结构。在30至50℃之间发生可逆的结构变化。然而，高于50℃时，胶束颗粒被破坏，蛋白质发生吸热的解折叠和变性，DSC显示其最高温度（Tmax）为52℃，焓为0.22 cal/g载脂蛋白B。DMPC - 载脂蛋白B复合物呈现出以24℃为中心的可逆热转变（ΔH = 3.34 Kcal/mol DMPC），这与DMPC烃链的有序 - 无序转变相关。在53 - 70℃范围内发生吸热转变（ΔH = 2.09 cal/g载脂蛋白B），如CD和浊度研究所示，这对应于蛋白质的解折叠 - 变性和颗粒破坏。CD表明，载脂蛋白B在囊泡环境中经历了一系列构象变化。主要变化发生在磷脂有序 - 无序转变的温度范围内。在37 - 60℃之间，其构象与在天然LDL中观察到的相似。
