Transcobalamin II receptor interacts with megalin in the renal apical brush border membrane.
Transcobalamin II receptor interacts with megalin in the renal apical brush border membrane.
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钴胺素 II 受体与肾尖刷状缘膜中的巨蛋白相互作用。
DOI：
10.1007/s00232-002-2007-3
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
Seetharam,B
中科院分区：
文献类型：
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作者：
Yammani,RR;Seetharam,S;Dahms,NM;Seetharam,B
纯化的人转钴胺素 II 受体 (TC II-R) 与巨蛋白结合，巨蛋白是一种 600 kDa 的内吞受体，在其配体转钴胺素 II (TC II) 存在和不存在的情况下，结合常数 Ka 为 66 nM，最大结合量为 1.1 摩尔 TC II-R/摩尔巨蛋白。对兔肾皮质顶刷状缘膜 (BBM) 的 Triton X-100 提取物进行免疫沉淀，然后进行免疫印迹，结果显示这两种蛋白质之间存在关联。 与钴胺素（Cbl；维生素 B12）复合的 35[S]-TC II 与琼脂糖巨蛋白亲和基质结合，当 TC II-R 与巨蛋白预结合时，结合增强 5 倍。巨蛋白抗血清抑制35[S]-TC II-Cbl与巨蛋白的TC II-R依赖性和非依赖性结合，而TC II-R抗血清仅抑制TC II-R依赖性结合。在循环巨蛋白抗血清的兔子中，肾尖 BBM 巨蛋白作为免疫复合物存在，但其水平没有改变。然而，TC II-R 和阳离子非依赖性甘露糖 6-磷酸受体 (CIMPR) 的蛋白水平急剧降低，TC II、白蛋白和其他低分子量蛋白的尿排泄量显着增加。这些结果表明巨蛋白含有 TC II-R 的独特单一高亲和力结合位点，并且它们在天然肾 BBM 中的结合对于包括 TC II 在内的许多蛋白质的肾小管重吸收非常重要。
Purified human transcobalamin II receptor (TC II-R) binds to megalin, a 600 kDa endocytic receptor with an association constant, Ka, of 66 nM and boundmaxof 1.1 mole of TC II-R/mole of megalin both in the presence and absence of its ligand, transcobalamin II (TC II). Immunoprecipitation followed by immunoblotting of Triton X-100 extracts of the apical brush border membrane (BBM) from rabbit renal cortex revealed association of these two proteins.35[S]-TC II complexed with cobalamin (Cbl; Vitamin B12) bound to Sepharose-megalin affinity matrix and the binding was enhanced 5-fold when TC II-R was prebound to megalin. Megalin antiserum inhibited both the TC II-R-dependent and -independent binding of35[S]-TC II-Cbl to megalin, while TC II-R antiserum inhibited only the TC II-R-dependent binding. In rabbits with circulating antiserum to megalin, renal apical BBM megalin was present as an immunecomplex, but its levels were not altered. However, the protein levels of both TC II-R and the cation-independent mannose 6-phosphate receptor (CIMPR) were drastically reduced and the urinary excretion of TC II, albumin, and other low-molecular weight proteins was significantly increased. These results suggest that megalin contains a distinct single high-affinity binding site for TC II-R and their association in the native renal BBM is important for tubular reabsorption of many proteins, including TC II.