Amyloid fibrils are polymeric structures originating from aggregation of misfolded proteins. In vivo, proteolysis may modulate amyloidogenesis and fibril stability. In light chain (AL) amyloidosis, fragmented light chains (LCs) are abundant components of amyloid deposits; however, site and timing of proteolysis are debated. Identification of the N and C termini of LC fragments is instrumental to understanding involved processes and enzymes. We investigated the N and C terminome of the LC proteoforms in fibrils extracted from the hearts of two AL cardiomyopathy patients, using a proteomic approach based on derivatization of N- and C-terminal residues, followed by mapping of fragmentation sites on the structures of native and fibrillar relevant LCs. We provide the first high-specificity map of proteolytic cleavages in natural AL amyloid. Proteolysis occurs both on the LC variable and constant domains, generating a complex fragmentation pattern. The structural analysis indicates extensive remodeling by multiple proteases, largely taking place on poorly folded regions of the fibril surfaces. This study adds novel important knowledge on amyloid LC processing: although our data do not exclude that proteolysis of native LC dimers may destabilize their structure and favor fibril formation, the data show that LC deposition largely precedes the proteolytic events documentable in mature AL fibrils.

中文翻译：

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心脏 AL 淀粉样变性中轻链断裂位点的质谱表征：蛋白水解时间的见解。

淀粉样原纤维是源自错误折叠蛋白质聚集的聚合结构。在体内，蛋白水解可以调节淀粉样蛋白生成和原纤维稳定性。在轻链 (AL) 淀粉样变性中，轻链片段 (LC) 是淀粉样蛋白沉积物的丰富成分；然而，蛋白水解的位点和时间存在争议。LC 片段的 N 和 C 末端的鉴定有助于理解所涉及的过程和酶。我们使用基于 N 和 C 末端残基衍生化的蛋白质组学方法，研究了从两名 AL 心肌病患者心脏中提取的原纤维中 LC 蛋白质形式的 N 和 C 末端，然后绘制了天然纤维结构上的断裂位点。和纤维相关的 LC。我们提供了天然 AL 淀粉样蛋白中第一个高特异性蛋白水解裂解图谱。蛋白水解作用发生在 LC 可变域和恒定域上，产生复杂的断裂模式。结构分析表明多种蛋白酶进行了广泛的重塑，主要发生在原纤维表面折叠不良的区域。这项研究增加了关于淀粉样蛋白 LC 处理的新的重要知识：尽管我们的数据不排除天然 LC 二聚体的蛋白水解可能会破坏其结构的稳定性并有利于原纤维的形成，但数据表明 LC 沉积很大程度上先于成熟 AL 原纤维中可记录的蛋白水解事件。