Cheresh D A, Harper J R
J Biol Chem. 1987 Feb 5;262(4):1434-7.
A major Arg-Gly-Asp-directed receptor on M21 human melanoma cells is a heterodimer of alpha and beta chains which under reducing conditions have molecular masses of 130 and 105 kDa, respectively. This receptor is one member of a large family of cell adhesion receptors that shares antigenic determinants with the vitronectin receptor of fibroblasts and the platelet IIb X IIIa complex. Both subunits of the M21 cell adhesion receptor acquire high mannose-type oligosaccharides that are processed before transport to the cell surface. In addition, the alpha chain undergoes a proteolytic cleavage step. Pulse-chase immunoprecipitation analysis demonstrates that, following its synthesis, the beta chain remains unbound to alpha chain for 1-2 h and in this free form is unable to bind an Arg-Gly-Asp containing heptapeptide. Conversely, the biosynthetic precursor of the alpha chain is fully capable of binding the Arg-Gly-Asp-containing peptide immediately after its synthesis. Thus, Arg-Gly-Asp recognition by one member of this cell adhesion receptor family requires its 130-kDa alpha chain which appears to be functional prior to post-translational modifications.
M21人黑素瘤细胞上一种主要的精氨酸 - 甘氨酸 - 天冬氨酸（Arg - Gly - Asp）导向受体是α链和β链的异二聚体，在还原条件下，其分子量分别为130 kDa和105 kDa。该受体是细胞黏附受体大家族的一员，与成纤维细胞的玻连蛋白受体和血小板IIb X IIIa复合物具有共同的抗原决定簇。M21细胞黏附受体的两个亚基都获得了高甘露糖型寡糖，这些寡糖在转运到细胞表面之前会进行加工。此外，α链会经历一个蛋白水解切割步骤。脉冲追踪免疫沉淀分析表明，β链在合成后1 - 2小时内仍未与α链结合，以这种游离形式无法结合含Arg - Gly - Asp的七肽。相反，α链的生物合成前体在合成后立即完全能够结合含Arg - Gly - Asp的肽。因此，这个细胞黏附受体家族的一个成员对Arg - Gly - Asp的识别需要其130 kDa的α链，该链在翻译后修饰之前似乎就具有功能。
