Ha-Duong Nguyêt-Thanh, Hémadi Miryana, Chikh Zohra, Chahine Jean-Michel El Hage
Laboratoire Interfaces, Traitements et Organisation des Systèmes, Université Paris-Diderot, CNRS UMR 7086, Bâtiment Lavoisier, Paris Cedex 13, France.
Biochem Soc Trans. 2008 Dec;36(Pt 6):1422-6. doi: 10.1042/BST0361422.
Transferrin receptor 1 (R) and human serum transferrin (T) are the two main actors in iron acquisition by the cell. R binds TFe(2) (iron-loaded transferrin), which allows its internalization in the cytoplasm by endocytosis. T also forms complexes with metals other than iron. In order to follow the iron-acquisition pathway, these metals should obey at least two essential rules: (i) formation of a strong complex with T; and (ii) interaction of this complex with R. In the present paper, we propose a general mechanism for the interaction of five metal-loaded Ts [Fe(III), Al(III), Bi(III), Ga(III) and Co(III)] with R and we discuss their potential incorporation by the iron-acquisition pathway. With iron- and cobalt-loaded Ts, the interaction of R takes place in two steps: the first is detected by the T-jump technique and occurs in the 100 micros range, whereas the second is slow and occurs in the hour range. Bi(III)- and Ga(III)-loaded Ts interact with R in a single fast kinetic step, which occurs in the 100-500 micros range. No interaction is detected between R and aluminium-saturated T. The fast steps are ascribed to the interaction of the C-lobe of metal-loaded T with the helical domain of R: dissociation constant, K'(1), of 0.50+/-0.07, 0.82+/-0.25, 4+/-0.4 and 1.10+/-0.12 microM for Fe(III), Co(III), Bi(III) and Ga(III) respectively. The second slow steps are ascribed to changes in the conformation of the protein-protein adducts which increase the stability to achieve, at thermodynamic equilibrium, an overall dissociation constant, K(1), of 2.3 and 25 nM for Fe(III) and Co(III) respectively. This last step occurs over several hours, whereas endocytosis takes place in several minutes. This implies that metal-loaded Ts are internalized with only the C-lobe interacting with R. This suggests that, despite a lower affinity for R when compared with TFe(2), some metal-loaded Ts can compete kinetically with TFe(2) for the interaction with R and thus follow the iron-acquisition pathway.
转铁蛋白受体1（R）和人血清转铁蛋白（T）是细胞获取铁的两个主要参与者。R结合TFe(2)（载铁转铁蛋白），使其通过内吞作用内化到细胞质中。T还会与铁以外的金属形成复合物。为了追踪铁的获取途径，这些金属应至少遵循两条基本规则：（i）与T形成强复合物；（ii）该复合物与R相互作用。在本文中，我们提出了五种载金属T [Fe(III)、Al(III)、Bi(III)、Ga(III)和Co(III)]与R相互作用的一般机制，并讨论了它们通过铁获取途径潜在的掺入情况。对于载铁和载钴的T，R的相互作用分两步进行：第一步通过T跳跃技术检测到，发生在100微秒范围内，而第二步较慢，发生在小时范围内。载Bi(III)和载Ga(III)的T与R在一个快速动力学步骤中相互作用，该步骤发生在100 - 500微秒范围内。未检测到R与铝饱和的T之间存在相互作用。快速步骤归因于载金属T的C叶与R的螺旋结构域的相互作用：Fe(III)、Co(III)、Bi(III)和Ga(III)的解离常数K'(1)分别为0.50±0.07、0.82±0.25、4±0.4和1.10±0.12微摩尔。第二个缓慢步骤归因于蛋白质 - 蛋白质加合物构象的变化，这种变化增加了稳定性，在热力学平衡时，Fe(III)和Co(III)的总解离常数K(1)分别为2.3和25纳摩尔。最后一步发生在几个小时内，而内吞作用在几分钟内发生。这意味着载金属的T仅通过C叶与R相互作用而被内化。这表明，尽管与TFe(2)相比对R的亲和力较低，但一些载金属的T可以在动力学上与TFe(2)竞争与R的相互作用，从而遵循铁获取途径。
