Mechanism of formation of the complex between transferrin and bismuth, and interaction with transferrin receptor 1
Mechanism of formation of the complex between transferrin and bismuth, and interaction with transferrin receptor 1
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DOI：
10.1021/bi048484p
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发表时间：
2004-11-23
期刊：
影响因子：
2.9
通讯作者：
Chahine, JME
中科院分区：
文献类型：
--
作者：
Miquel, G;Nekaa, T;Chahine, JME
在 pH 7.4-8.9 下研究了单次氮基三乙酸铋 (BiL) 与人血清转铁蛋白之间 Bi(III) 交换的动力学和热力学，以及负载铋的转铁蛋白与转铁蛋白受体 1 (TFR) 之间相互作用的动力学和热力学。铋在 BiL 和人血清脱铁转铁蛋白 C 位点之间快速交换，与碳酸氢盐相互作用，产生中间复合物，其有效平衡常数 K-1 为 6 +/- 4，直接二阶速率常数 k(1) 为 (2.45 +/- 0.20) x 10(5) M-1 s(-1)，反向二阶速率常数 k(-1) 为 (1.5 +/- 0.5) x 10(6) M-1 s(-1)。中间复合物失去质子解离常数 K-1a 为 2.4 +/- 1 nM 的单个质子，产生第一个动力学产物。然后，该产物经历构象修饰，然后以一阶速率常数 k(2) = 25 +/- 1.5 s(-1) 进行两次质子损失，产生第二个动力学中间体，该中间体又经历构象的最后修饰，产生最终状态的铋饱和转铁蛋白。最后一个过程速率控制蛋白质 N 位点对 Bi(III) 的摄取，并且独立于实验参数，具有 (3 +/- 1) x 10(-2) s(-1) 的恒定倒数弛豫时间 tau(3)(-1)。铋的吸收机制与铁的吸收机制不同，并且可能不涉及铁吸收时从开放到闭合构象的相同转变。载铋转铁蛋白与 TFR 的相互作用发生在一个非常快的动力学步骤中，解离常数 K-d 为 4 +/- 0.4 muM，二阶速率常数 k(d) 为 (2.2 +/- 1.5) x 10(8) M-1 s(-1)，一阶速率常数 k(-d) 为 900 +/- 400 s(-1)。该机制与用全转铁蛋白铁观察到的机制不同，并且意味着 TFR 和负载铋的转铁蛋白之间的相互作用可能发生在对转铁蛋白和 HFE 的 C 位点具有特异性的受体螺旋结构域上。讨论了转铁蛋白受体介导的铁获取途径掺入铋的相关性。
The kinetics and thermodynamics of Bi(III) exchange between bismuth mononitrilotriacetate (BiL) and human serum transferrin as well as those of the interaction between bismuth-loaded transferrin and transferrin receptor 1 (TFR) were investigated at pH 7.4-8.9. Bismuth is rapidly exchanged between BiL and the C-site of human serum apotransferrin in interaction with bicarbonate to yield an intermediate complex with an effective equilibrium constant K-1 of 6 +/- 4, a direct second-order rate constant k(1) of (2.45 +/- 0.20) x 10(5) M-1 s(-1), and a reverse second-order rate constant k(-1) of (1.5 +/- 0.5) x 10(6) M-1 s(-1). The intermediate complex loses a single proton with a proton dissociation constant K-1a of 2.4 +/- 1 nM to yield a first kinetic product. This product then undergoes a modification in its conformation followed by two proton losses with a first-order rate constant k(2) = 25 +/- 1.5 s(-1) to produce a second kinetic intermediate, which in turn undergoes a last modification in the conformation to yield the bismuth-saturated transferrin in its final state. This last process rate-controls Bi(III) uptake by the N-site of the protein and is independent of the experimental parameters with a constant reciprocal relaxation time tau(3)(-1) of (3 +/- 1) x 10(-2) s(-1). The mechanism of bismuth uptake differs from that of iron and probably does not involve the same transition in conformation from open to closed upon iron uptake. The interaction of bismuth-loaded transferrin with TFR occurs in a single very fast kinetic step with a dissociation constant K-d of 4 +/- 0.4 muM, a second-order rate constant k(d) of (2.2 +/- 1.5) x 10(8) M-1 s(-1), and a first-order rate constant k(-d) Of 900 +/- 400 s(-1). This mechanism is different from that observed with the ferric holotransferrin and implies that the interaction between TFR and bismuth-loaded transferrin probably takes place on the helical domain of the receptor which is specific for the C-site of transferrin and HFE. The relevance of bismuth incorporation by the transferrin receptor-mediated iron acquisition pathway is discussed.