HFE and transferrin directly compete for transferrin receptor in solution and at the cell surface
HFE and transferrin directly compete for transferrin receptor in solution and at the cell surface
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DOI：
10.1074/jbc.m401467200
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发表时间：
2004-06-11
影响因子：
4.8
通讯作者：
Björkman, PJ
中科院分区：
文献类型：
--
作者：
Giannetti, AM;Björkman, PJ
转铁蛋白受体（TfR）是结合血清铁转运蛋白转铁蛋白（Fe-Tf）和HFE两者的二聚体细胞表面蛋白，HFE是在患有铁超负荷病症遗传性血色病的患者中突变的蛋白质。HFE和Fe-Tf可以同时与TfR结合形成三元复合物，但HFE与TfR的结合降低了Fe-Tf/TfR相互作用的表观亲和力。这种明显的亲和力降低可能是由于HFE和Fe-Tf之间直接竞争它们在每个TfR多肽链上的重叠结合位点，负协同性，或两者的组合。为了探索亲和力降低的机制，我们构建了一个异源二聚体TfR，其含有突变，使得一个TfR链仅结合HFE，另一个仅结合Fe-Tf。使用可溶性TfR的异二聚体形式的结合研究表明，TfR在异向性配体结合中不表现出协同性，这表明HFE对铁稳态的部分或全部影响来自与Fe-Tf竞争TfR结合。使用转染细胞系的实验证明了这种竞争在改变HFE运输模式中的生理作用。
Transferrin receptor (TfR) is a dimeric cell surface protein that binds both the serum iron transport protein transferrin (Fe-Tf) and HFE, the protein mutated in patients with the iron overload disorder hereditary hemochromatosis. HFE and Fe-Tf can bind simultaneously to TfR to form a ternary complex, but HFE binding to TfR lowers the apparent affinity of the Fe-Tf/TfR interaction. This apparent affinity reduction could result from direct competition between HFE and Fe-Tf for their overlapping binding sites on each TfR polypeptide chain, from negative cooperativity, or from a combination of both. To explore the mechanism of the affinity reduction, we constructed a heterodimeric TfR that contains mutations such that one TfR chain binds only HFE and the other binds only Fe-Tf. Binding studies using a heterodimeric form of soluble TfR demonstrate that TfR does not exhibit cooperativity in heterotropic ligand binding, suggesting that some or all of the effects of HFE on iron homeostasis result from competition with Fe-Tf for TfR binding. Experiments using transfected cell lines demonstrate a physiological role for this competition in altering HFE trafficking patterns.