DIMERIZATION OF TRANSCOBALAMIN II RECEPTOR

转钴胺素II受体（TC II-R）作为单体和一个受体存在。 微粒体中分子量为62和124 kDa的二聚体， 质膜，分别。 在体内，纯TC II-R单体 在插入到卵PC/胆固醇（41）脂质体中时二聚化。 的 目前的研究是为了确定TC II-R的作用机制 二聚化。 酶促去糖基化（45-47 kDa）和 成熟的纯TC II-R（62 kDa）表现出最佳结合， 分别形成分子量为95和124 kDa的二聚体， 22岁？C与含有至少10摩尔%的卵PC囊泡结合 胆固醇。 成熟的受体在插入后也二聚化， 二肉豆蔻酰磷脂酰胆碱囊泡5？C在没有 胆固醇还是22？C与使用脂质制备的脂质囊泡 从血浆中提取，而不是微粒体膜。 胆固醇 天然肠质膜的耗竭或其富集 微粒体膜导致124个细胞的原位转化， kDa二聚体转化为62 kDa单体或单体转化为二聚体形式， 分别 用磷脂酶A2处理质膜 导致受体二聚体形式的原位转化 单体形式。 使用1-棕榈酰的自旋标记研究，12 doxylsteroyl PC显示与TC II-R的相互作用增加 围绕探测器。 基于这些结果，我们建议， TC II-R的二聚化是1）通过其与一种 刚性更有序的脂质双层膜; 2）在质膜中， 受胆固醇水平调节; 3）独立于 糖基化介导的折叠。

Transcobalamin II receptor (TC II-R) exists as a monomer and a dimer of molecular masses of 62 and 124 kDa in the microsomal and plasma membranes, respectively. In vivo, pure TC II-R monomer dimerizes upon insertion into egg PC/cholesterol (41) liposomes. The current studies were carried out to define the mechanism of TC II-R dimerization. Both enzymatically deglycosylated (45-47 kDa) and mature pure TC II-R (62 kDa) demonstrated optimal association and formed dimers of molecular mass of 95 and 124 kDa, respectively, at 22?C in association with egg PC vesicles containing at least 10 mole% of cholesterol. Mature receptor also dimerized upon insertion into dimyristoyl phosphatidylcholine vesicles at 5?C in the absence of cholesterol or at 22?C with lipid vesicles prepared using lipid extract from the plasma, but not microsomal membranes. Cholesterol depletion of native intestinal plasma membranes or its enrichment of microsomal membranes resulted in the in situ conver sio n of the 124 kDa dimer to the 62 kDa monomer or of the monomer into the dimer form, respectively. Treatment of the plasma membranes with phospholipase A2 resulted in the in situ conversion of the dimer form of the receptor to the monomer form. Spin-label studies using 1-palmitoyl, 12 doxylsteroyl PC revealed that interactions with TC II-R increased order around the probe. Based on these results, we suggest that dimerization of TC II-R is 1) mediated by its interactions with a rigidly more ordered lipid bilayer membrane; 2) in plasma membranes, is regulated by cholesterol levels; and 3) is independent of glycosylation-mediated folding.