Haptoglobin Binding Stabilizes Hemoglobin Ferryl Iron and the Globin Radical on Tyrosine β145
Haptoglobin Binding Stabilizes Hemoglobin Ferryl Iron and the Globin Radical on Tyrosine β145
复制标题
DOI：
10.1089/ars.2012.4547
复制
发表时间：
2013-06-01
影响因子：
6.6
通讯作者：
Alayash, Abdu I.
中科院分区：
文献类型：
--
作者：
Cooper, Chris E.;Schaer, Dominik J.;Alayash, Abdu I.
目的：血红蛋白（Hb）从红细胞中释放出来后具有毒性。急性期蛋白结合珠蛋白（Hp）与Hb强烈结合，并减少对Hb本身以及周围蛋白质和脂质的氧化损伤。然而，支持Hp保护的分子机制迄今尚不清楚。本研究的目的是使用电子顺磁共振（EPR）光谱，停流光学分光光度法，和定点突变，以探讨机制，特别是特定的酪氨酸残基在这种保护的作用。结果：在过氧化物的挑战血红蛋白产生活性氧化中间体的形式铁血红素和珠蛋白自由基。Hp结合增加了铁基形成的稳态水平在血红蛋白催化的脂质过氧化反应，而在同一时间显着抑制整体反应速率。在不存在脂质和存在外部还原剂的情况下也可以看到这种增强的铁基稳定性。Hp结合不伴随铁基质子化的pK降低;质子化的铁基物质仍然形成，但本质上反应性较低。铁基稳定伴随着过氧化物诱导的酪氨酸自由基浓度的显着增加。EPR光谱参数和诱变研究表明，这个自由基是位于酪氨酸145，倒数第二个C-末端氨基酸的β血红蛋白亚基。创新：Hp结合降低了Hb的铁基铁和自由基反应性。结论：Hp在脉管系统中保护免受Hb诱导的损伤，不是通过防止血红素氧化剂的主要反应性，而是通过使所得蛋白质产物损伤较小。抗氧化剂。氧化还原信号。18，2264-2273。
Aim: Hemoglobin (Hb) becomes toxic when released from the erythrocyte. The acute phase protein haptoglobin (Hp) binds avidly to Hb and decreases oxidative damage to Hb itself and to the surrounding proteins and lipids. However, the molecular mechanism underpinning Hp protection is to date unclear. The aim of this study was to use electron paramagnetic resonance (EPR) spectroscopy, stopped flow optical spectrophotometry, and site-directed mutagenesis to explore the mechanism and specifically the role of specific tyrosine residues in this protection. Results: Following peroxide challenge Hb produces reactive oxidative intermediates in the form of ferryl heme and globin free radicals. Hp binding increases the steady state level of ferryl formation during Hb-catalyzed lipid peroxidation, while at the same time dramatically inhibiting the overall reaction rate. This enhanced ferryl stability is also seen in the absence of lipids and in the presence of external reductants. Hp binding is not accompanied by a decrease in the pK of ferryl protonation; the protonated ferryl species still forms, but is intrinsically less reactive. Ferryl stabilization is accompanied by a significant increase in the concentration of the peroxide-induced tyrosine free radical. EPR spectral parameters and mutagenesis studies suggest that this radical is located on tyrosine 145, the penultimate C-terminal amino acid on the beta Hb subunit. Innovation: Hp binding decreases both the ferryl iron and free radical reactivity of Hb. Conclusion: Hp protects against Hb-induced damage in the vasculature, not by preventing the primary reactivity of heme oxidants, but by rendering the resultant protein products less damaging. Antioxid. Redox Signal. 18, 2264-2273.