Vassiliou G, Stanley K K
Heart Research Institute, Camperdown, Sydney, New South Wales, Australia.
J Biol Chem. 1994 May 27;269(21):15172-8.
We have investigated the proposal that the receptor-associated protein (RAP) of the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor binds to heparan sulfate proteoglycans (HSP). 125I-RAP binds to two sites on the surface of fibroblasts as follows: a high affinity site with a Kd of 1.4 nM and a low affinity site (Kd = 188 nM) with a capacity of more than 1000-fold the maximum amount of lipoprotein receptor-related protein/alpha 2-macroglobulin receptor on the cell surface. 125I-RAP binding to the low affinity site was abolished by heparin or Suramin. However, maximal digestion of the glycosaminoglycan chains of HSP with heparinase or culturing the cells in chlorate, an inhibitor of proteoglycan sulfation, did not affect the binding of 125I-RAP or of 125I-labeled, methylamine-activated alpha 2-macroglobulin. Comparison of 125I-RAP degradation at two different concentrations suggests that the low affinity, high capacity site on the surface of human fibroblasts participates in the endocytosis of 125I-RAP. The nature of the low affinity site remains to be elucidated, but we can exclude the glycosaminoglycan chains of HSP.
我们研究了低密度脂蛋白受体相关蛋白/α2-巨球蛋白受体的受体相关蛋白（RAP）与硫酸乙酰肝素蛋白聚糖（HSP）结合的提议。125I-RAP与成纤维细胞表面的两个位点结合，具体如下：一个高亲和力位点，Kd为1.4 nM；一个低亲和力位点（Kd = 188 nM），其容量比细胞表面脂蛋白受体相关蛋白/α2-巨球蛋白受体的最大量高1000倍以上。肝素或苏拉明可消除125I-RAP与低亲和力位点的结合。然而，用肝素酶对HSP的糖胺聚糖链进行最大程度的消化，或在氯酸盐（蛋白聚糖硫酸化抑制剂）中培养细胞，均不影响125I-RAP或125I标记的甲胺激活的α2-巨球蛋白的结合。对两种不同浓度下125I-RAP降解的比较表明，人成纤维细胞表面的低亲和力、高容量位点参与了125I-RAP的内吞作用。低亲和力位点的性质尚待阐明，但我们可以排除HSP的糖胺聚糖链。
