The synergistic anion-binding sites of human transferrin: chemical and physiological effects of site-directed mutagenesis.
The synergistic anion-binding sites of human transferrin: chemical and physiological effects of site-directed mutagenesis.
复制标题
人转铁蛋白的协同阴离子结合位点：定点诱变的化学和生理效应。
DOI：
10.1021/bi0160258
复制
发表时间：
2002
期刊：
影响因子：
2.9
通讯作者：
Aisen,Philip
中科院分区：
文献类型：
--
作者：
Zak,Olga;Ikuta,Katsuya;Aisen,Philip
所有转铁蛋白的一个决定性特征是铁结合绝对依赖于协同阴离子的结合，通常但不一定是碳酸盐。它作为铁和蛋白质之间的桥接配体，完成铁的配位要求，将必需的金属锁定在其结合位点。为了研究协同阴离子在人转铁蛋白的铁结合和供铁特性中的作用，我们选择性地突变了阴离子结合的苏氨酸和精氨酸配体，这些配体是静电和氢键网络的重要组成部分，将协同阴离子与蛋白质结合在一起。任何一种配体的保存都足以维持阴离子结合，从而维持突变叶中的铁结合。精氨酸是一种比苏氨酸更强的配体，它的损失削弱了碳酸盐和铁的结合，但保持了硝化三乙酸盐作为碳酸盐替代品的能力。替换这两种配体会消除阴离子结合，从而消除受影响叶中的铁结合。任何肺叶中阴离子结合的缺失导致单铁蛋白仅在另一侧肺叶中以正常方式结合铁。这两种单铁蛋白都能够依赖转铁蛋白受体结合并向K562细胞提供铁，但仅在n叶中携带铁的蛋白占用受体减少。
A defining feature of all transferrins is the absolute dependence of iron binding on the concomitant binding of a synergistic anion, normally but not necessarily carbonate. Acting as a bridging ligand between iron and protein, it completes the coordination requirements of iron to lock the essential metal in its binding site. To investigate the role of the synergistic anion in the iron-binding and iron-donating properties of human transferrin, a bilobal protein with an iron binding site in each lobe, we have selectively mutated the anion-binding threonine and arginine ligands that form an essential part of the electrostatic and hydrogen-bonding network holding the synergistic anion to the protein. Preservation of either ligand is sufficient to maintain anion binding, and therefore iron binding, in the mutated lobe. Arginine is a stronger ligand than threonine, and its loss weakens carbonate and therefore iron binding, but maintains the ability of nitrilotriacetate to serve as a carbonate surrogate. Replacement of both ligands abolishes anion binding and consequently iron binding in the affected lobe. Loss of anion binding in either lobe results in a monoferric protein binding iron in normal fashion only in the opposite lobe. Both monoferric proteins are capable of transferrin receptor-dependent binding and iron donation to K562 cells, but with diminished receptor occupancy by the protein bearing iron only in the N-lobe.