Many neurodegenerative diseases feature misfolded proteins that propagate via templated conversion of natively folded molecules. However, crucial questions about how such prion-like conversion occurs and what drives it remain unsolved, partly because technical challenges have prevented direct observation of conversion for any protein. We observed prion-like conversion in single molecules of superoxide dismutase-1 (SOD1), whose misfolding is linked to amyotrophic lateral sclerosis. Tethering pathogenic misfolded SOD1 mutants to wild-type molecules held in optical tweezers, we found that the mutants vastly increased misfolding of the wild-type molecule, inducing multiple misfolded isoforms. Crucially, the pattern of misfolding was the same in the mutant and converted wild-type domains and varied when the misfolded mutant was changed, reflecting the templating effect expected for prion-like conversion. Ensemble measurements showed decreased enzymatic activity in tethered heterodimers as conversion progressed, mirroring the single-molecule results. Antibodies sensitive to disease-specific epitopes bound to the converted protein, implying that conversion produced disease-relevant misfolded conformers.

许多神经退行性疾病都以错误折叠的蛋白质为特征，这些蛋白质通过天然折叠分子的模板化转换而传播。然而，关于这种类似朊病毒的转化如何发生以及驱动其发生的因素的关键问题仍未解决，部分原因是技术挑战阻碍了对任何蛋白质转化的直接观察。我们观察到超氧化物歧化酶-1 (SOD1) 单分子中的朊病毒样转化，其错误折叠与肌萎缩侧索硬化症有关。将致病性错误折叠 SOD1 突变体与光镊中的野生型分子连接起来，我们发现突变体大大增加了野生型分子的错误折叠，诱导多种错误折叠亚型。至关重要的是，错误折叠模式在突变体和转化的野生型结构域中是相同的，并且当错误折叠突变体改变时发生变化，反映了朊病毒样转化预期的模板效应。整体测量显示，随着转化的进行，束缚异二聚体中的酶活性降低，这反映了单分子结果。对疾病特异性表位敏感的抗体与转化的蛋白质结合，这意味着转化产生了与疾病相关的错误折叠构象异构体。