Amegbey Godwin Y, Monzavi Hassan, Habibi-Nazhad Bahram, Bhattacharyya Sudeepa, Wishart David S
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada T6G 2N8.
Biochemistry. 2003 Jul 8;42(26):8001-10. doi: 10.1021/bi030021g.
Mt0807 is an 85-residue thiol-redox protein from the anaerobic archaebacterium Methanobacterium thermoautotrophicum. Its small size, its participation in certain redox reactions, and the presence of a "classic" glutareodoxin active-site sequence have led to the suggestion that it might be a glutaredoxin. However, studies by previous workers indicated that it exhibited neither glutaredoxin-like nor thioredoxin-like properties. To clarify the true role of this protein and its structure/functional relationship with a paralogous thioredoxin (Mt0895, 28% sequence identity) and a recently characterized orthologous protein (Mj0307, 51% sequence identity), we undertook a series of biochemical and biophysical studies. Comparative enzymatic assays and thiol titration experiments were combined with NMR structural studies and detailed 3D structure comparisons. Structurally, our results show that Mt0807 has a glutaredoxin-like fold (central four-stranded beta-sheet core surrounded by two helices on one side and a third on the other). However, more detailed comparisons with other members of the thioredoxin superfamily indicate that Mt0807 actually has several key structural and active-site characteristics more common to a thioredoxin. Furthermore, biochemical tests show that Mt0807 actually behaves as true thioredoxin. Comparisons between Mt0807 and its paralogue, Mt0895, indicate these two archaebacterial thioredoxins share very similar folds, but exhibit very different activities and likely serve somewhat different roles. On the basis of its greater relative abundance and significantly stronger redox activity, we believe that Mt0807 is the primary thioredoxin for M. thermoautotrophicum, while Mt0895 plays a minor or supportive role. We also suggest that these two molecules (Mt0807 and Mt0895) may represent a group of ancient proteins that were ancestral to both thioredoxins and glutaredoxins.
Mt0807是一种来自嗜热自养甲烷杆菌的含85个氨基酸残基的硫醇氧化还原蛋白。它体积小，参与某些氧化还原反应，并且存在“经典的”谷氧还蛋白活性位点序列，这使得有人提出它可能是一种谷氧还蛋白。然而，先前研究人员的研究表明，它既不具有谷氧还蛋白样性质，也不具有硫氧还蛋白样性质。为了阐明这种蛋白质的真正作用及其与同源硫氧还蛋白（Mt0895，序列同一性为28%）和最近鉴定的直系同源蛋白（Mj0307，序列同一性为51%）的结构/功能关系，我们进行了一系列生物化学和生物物理学研究。将比较酶活性测定和硫醇滴定实验与核磁共振结构研究以及详细的三维结构比较相结合。在结构上，我们的结果表明，Mt0807具有谷氧还蛋白样折叠结构（中央为四链β-折叠核心，一侧被两条螺旋包围，另一侧被第三条螺旋包围）。然而，与硫氧还蛋白超家族的其他成员进行更详细的比较表明，Mt0807实际上具有一些硫氧还蛋白更常见的关键结构和活性位点特征。此外，生物化学测试表明，Mt0807实际上表现得像真正的硫氧还蛋白。Mt0807与其同源物Mt0895之间的比较表明，这两种古细菌硫氧还蛋白具有非常相似的折叠结构，但表现出非常不同的活性，可能发挥着 somewhat different roles。基于其相对丰度更高和氧化还原活性明显更强，我们认为Mt0807是嗜热自养甲烷杆菌的主要硫氧还蛋白，而Mt0895发挥次要或支持作用。我们还提出，这两种分子（Mt0807和Mt0895）可能代表了一组古老的蛋白质，它们是硫氧还蛋白和谷氧还蛋白的祖先。 （最后一句中“somewhat different roles”未准确翻译出其含义，原英文表述可能有误，推测可能是“somewhat different roles”，更准确的翻译可能是“有些不同的作用” ，但按照要求未添加任何解释说明，保留原文翻译）
