Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República 127, 2780-756 Oeiras, Portugal.
Biochem J. 2010 Feb 9;426(2):197-203. doi: 10.1042/BJ20091612.
Frataxin is a highly conserved mitochondrial protein whose deficiency in humans results in Friedreich's ataxia (FRDA), an autosomal recessive disorder characterized by progressive ataxia and cardiomyopathy. Although its cellular function is still not fully clear, the fact that frataxin plays a crucial role in Fe-S assembly on the scaffold protein Isu is well accepted. In the present paper, we report the characterization of eight frataxin variants having alterations on two putative functional regions: the alpha1/beta1 acidic ridge and the conserved beta-sheet surface. We report that frataxin iron-binding capacity is quite robust: even when five of the most conserved residues from the putative iron-binding region are altered, at least two iron atoms per monomer can be bound, although with decreased affinity. Furthermore, we conclude that the acidic ridge is designed to favour function over stability. The negative charges have a functional role, but at the same time significantly impair frataxin's stability. Removing five of those charges results in a thermal stabilization of approximately 24 degrees C and reduces the inherent conformational plasticity. Alterations on the conserved beta-sheet residues have only a modest impact on the protein stability, highlighting the functional importance of residues 122-124.
铁蛋白是一种高度保守的线粒体蛋白，其在人类中的缺乏导致弗里德里希共济失调（FRDA），这是一种常染色体隐性疾病，其特征是进行性共济失调和心肌病。尽管其细胞功能尚不完全清楚，但铁蛋白在支架蛋白 Isu 上参与 Fe-S 组装中起着至关重要的作用这一事实已被广泛接受。在本文中，我们描述了对两个假定功能区域（α1/β1 酸性脊和保守的β-折叠表面）发生改变的 8 种铁蛋白变体的特征。我们报告说，铁蛋白的铁结合能力非常强：即使假定的铁结合区域的 5 个最保守的残基发生改变，至少每个单体可以结合两个铁原子，尽管亲和力降低。此外，我们得出结论，酸性脊的设计旨在促进功能而不是稳定性。负电荷具有功能作用，但同时会严重损害铁蛋白的稳定性。去除其中的 5 个电荷会导致大约 24°C 的热稳定性增加，并降低固有构象灵活性。对保守的β-折叠残基的改变仅对蛋白质稳定性产生适度影响，突出了残基 122-124 的功能重要性。
