Anantharamaiah G M, Hughes T A, Iqbal M, Gawish A, Neame P J, Medley M F, Segrest J P
Department of Medicine, University of Alabama, Birmingham 35294.
J Lipid Res. 1988 Mar;29(3):309-18.
Purified apolipoprotein A-I has been separated by reversed-phase high performance liquid chromatography (HPLC) into multiple peaks and these peaks have been characterized. One peak, apoA-Ib had a relatively longer retention time on HPLC but its retention time could be shortened by treatment by hydrogen peroxide. CNBr cleavage studies indicated that the differences in apoA-Ib and in its oxidation product, apoA-Ia, were due to the different oxidation states of methionine. This phenomenon was also observed in apoA-II, where methionine oxidation produced two more forms of this apolipoprotein in addition to the native form. These isomers were found to have different secondary structures and affinities for lipid. Model peptide analogs of the amphipathic helix with the same sequence but with methionine and methionine sulfoxide at the nonpolar face of the amphipathic helix were synthesized and studied. It was found that the lipid affinities of these synthetic peptide isomers were very different. They also differed in their secondary structures as studied by circular dichroism (CD). We propose that methionine oxidation introduces hydrophilic residues at the nonpolar face of the amphipathic helical domains of these apolipoproteins and, therefore, alters their secondary structure and lipid affinity.
纯化的载脂蛋白A-I已通过反相高效液相色谱（HPLC）分离为多个峰，并对这些峰进行了表征。其中一个峰，即载脂蛋白A-Ib，在HPLC上具有相对较长的保留时间，但用过氧化氢处理可缩短其保留时间。溴化氰裂解研究表明，载脂蛋白A-Ib与其氧化产物载脂蛋白A-Ia的差异是由于甲硫氨酸的氧化状态不同。在载脂蛋白A-II中也观察到了这种现象，其中甲硫氨酸氧化除了产生天然形式的载脂蛋白A-II外，还产生了另外两种形式。发现这些异构体具有不同的二级结构和对脂质的亲和力。合成并研究了具有相同序列但在两亲性螺旋的非极性面上含有甲硫氨酸和甲硫氨酸亚砜的两亲性螺旋的模型肽类似物。发现这些合成肽异构体的脂质亲和力非常不同。通过圆二色性（CD）研究，它们在二级结构上也有所不同。我们提出，甲硫氨酸氧化在这些载脂蛋白的两亲性螺旋结构域的非极性面上引入了亲水性残基，因此改变了它们的二级结构和脂质亲和力。
