Abstract：
Tau is a neuronal protein involved in axonal stabilization; however under pathological conditions, it triggers the deposition of insoluble neurofibrillary tangles, which are one of the biomarkers for Alzheimer\'s disease. The factors that might influence the fibrillation process are i) two cysteine residues in two pseudorepetitive regions, called R2 and R3, which can modulate protein-protein interaction via disulfide cross-linking; ii) an increase of reactive oxygen species affecting the post-translational modification of tau; and iii) cytotoxic levels of metals, especially ferric-heme (hemin), in hemolytic processes. Herein, we investigated how the cysteine-containing R3 peptide (R3C) and its Cys→Ala mutant (R3A) interact with hemin and how their binding affects the oxidative damage of the protein. The calculated binding constants are remarkably higher for the hemin-R3C complex (LogK1 = 5.90; LogK2 = 5.80) with respect to R3A (LogK1 = 4.44; LogK2 < 2), although NMR and CD investigations excluded the direct binding of cysteine as an iron axial ligand. Both peptides increase the peroxidase-like activity of hemin toward catecholamines and phenols, with a double catalytic efficiency detected for hemin-R3C systems. Moreover, the presence of cysteine significantly alters the susceptibility of R3 toward oxidative modifications, easily resulting in peptide dopamination and formation of cross-linked S-S derivatives.
摘要：
Tau是一种参与轴突稳定的神经元蛋白;然而在病理条件下，它引发不溶性神经原纤维缠结的沉积，是阿尔茨海默病的生物标志物之一。可能影响纤颤过程的因素是i）两个假重复区域中的两个半胱氨酸残基，称为R2和R3，可以通过二硫键交联调节蛋白质-蛋白质相互作用；ii）活性氧的增加影响tau的翻译后修饰；iii）金属的细胞毒性水平，尤其是铁血红素（血红素），在溶血过程中。在这里，我们研究了含半胱氨酸的R3肽（R3C）及其Cys→Ala突变体（R3A）如何与血红素相互作用，以及它们的结合如何影响蛋白质的氧化损伤。相对于R3A（LogK1=4.44；LogK2<2），血红素-R3C复合物（LogK1=5.90；LogK2=5.80）的计算结合常数明显更高，尽管NMR和CD研究排除了半胱氨酸作为铁轴配体的直接结合。两种肽都会增加血红素对儿茶酚胺和酚的过氧化物酶样活性，对血红素-R3C系统检测到双重催化效率。此外，半胱氨酸的存在显著改变了R3对氧化修饰的敏感性，容易导致肽掺杂和形成交联的S-S衍生物。
