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Exposure of Solvent-Inaccessible Regions in the Amyloidogenic Protein Human SOD1 Determined by Hydroxyl Radical Footprinting.
Journal of the American Society for Mass Spectrometry ( IF 3.2 ) Pub Date : 2018-10-16 , DOI: 10.1007/s13361-018-2075-y
Yuewei Sheng 1 , Joseph Capri 2 , Alan Waring 3 , Joan Selverstone Valentine 1 , Julian Whitelegge 2, 4
Affiliation  

Solvent-accessibility change plays a critical role in protein misfolding and aggregation, the culprit for several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Mass spectrometry-based hydroxyl radical (·OH) protein footprinting has evolved as a powerful and fast tool in elucidating protein solvent accessibility. In this work, we used fast photochemical oxidation of protein (FPOP) hydroxyl radical (·OH) footprinting to investigate solvent accessibility in human copper-zinc superoxide dismutase (SOD1), misfolded or aggregated forms of which underlie a portion of ALS cases. ·OH-mediated modifications to 56 residues were detected with locations largely as predicted based on X-ray crystallography data, while the interior of SOD1 β-barrel is hydrophobic and solvent-inaccessible and thus protected from modification. There were, however, two notable exceptions-two closely located residues inside the β-barrel, predicted to have minimal or no solvent accessibility, that were found modified by FPOP (Phe20 and Ile112). Molecular dynamics (MD) simulations were consistent with differential access of peroxide versus quencher to SOD1's interior complicating surface accessibility considerations. Modification of these two residues could potentially be explained either by local motions of the β-barrel that increased peroxide/solvent accessibility to the interior or by oxidative events within the interior that might include long-distance radical transfer to buried sites. Overall, comparison of modification patterns for the metal-free apoprotein versus zinc-bound forms demonstrated that binding of zinc protected the electrostatic loop and organized the copper-binding site. Our study highlights SOD1 hydrophobic groups that may contribute to early events in aggregation and discusses caveats to surface accessibility conclusions. Graphical Abstract.

中文翻译:

由羟自由基足迹确定的淀粉样蛋白人类SOD1中溶剂不可及区域的暴露。

溶剂可及性的改变在蛋白质错误折叠和聚集中起着至关重要的作用,蛋白质是错误折叠和聚集的元凶,而蛋白质是包括肌萎缩性侧索硬化症(ALS)在内的几种神经变性疾病的元凶。基于质谱的羟基自由基(·OH)蛋白印迹已成为阐明蛋白溶剂可及性的强大而快速的工具。在这项工作中,我们使用蛋白质(FPOP)羟自由基(·OH)足迹的快速光化学氧化来研究人类铜锌超氧化物歧化酶(SOD1)中溶剂的可及性,其中错折叠或聚集形式是部分ALS病例的基础。·检测到OH介导的对56个残基的修饰,其位置在很大程度上是根据X射线晶体学数据预测的,而SOD1β-桶的内部是疏水性的,溶剂不可及,因此可以防止修饰。但是,有两个显着的例外-β桶内的两个紧密定位的残基,被预测具有最小或没有溶剂可及性,这些残基被FPOP修饰(Phe20和Ile112)。分子动力学(MD)模拟与过氧化物和淬灭剂对SOD1内部的差异进入相一致,这使表面可达性考虑变得复杂。这两个残基的修饰可能通过β桶的局部运动(可能增加过氧化物/溶剂对内部的可及性)或内部的氧化事件(可能包括从长距离自由基转移到掩埋位点)来解释。全面的,比较无金属载脂蛋白和锌结合形式的修饰方式,结果表明锌的结合保护了静电环并组织了铜结合位点。我们的研究强调了SOD1疏水基团可能有助于聚集的早期事件,并讨论了对表面可及性结论的警告。图形概要。
更新日期:2018-10-16
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