Probing the fibrillation of lysozyme by nanoscale-infrared spectroscopy

Amyloid fibrillation is the root cause of several neuro as well as non-neurological disorders. Understanding the molecular basis of amyloid aggregate formation is crucial for deciphering various neurodegenerative diseases. In our study, we have examined the lysozyme fibrillation process using nano-infrared spectroscopy (nanoIR). NanoIR enabled us to investigate both structural and chemical characteristics of lysozyme fibrillar species concurrently. The spectroscopic results indicate that lysozyme transformed into a fibrillar structure having mainly parallel β-sheets, with almost no antiparallel β-sheets. Features such as protein stiffness have a good correlation with obtained secondary structural information showing the state of the protein within the fibrillation state. The structural and chemical details were compared with transmission electron microscopy (TEM) and circular dichroism (CD). We have utilized nanoIR and measured infrared spectra to characterize lysozyme amyloid fibril structures in terms of morphology, molecular structure, secondary structure content, stability, and size of the cross-β core. We have shown that the use of nanoIR can complement other biophysical studies to analyze the aggregation process and is particularly useful for studying proteins involved in aggregation to help in designing molecules against amyloid aggregation. Specifically, the nanoIR spectra afford higher resolution information and a characteristic fingerprint for determining states of aggregation. Communicated by Ramaswamy H. Sarma

淀粉样纤维化（amyloid fibrillation）是多种神经及非神经疾病的核心致病机制。解析淀粉样聚集体形成的分子基础，对于阐明各类神经退行性疾病的病理机制至关重要。本研究采用纳米红外光谱（nano-infrared spectroscopy，简称nanoIR）考察了溶菌酶的纤维化过程。该技术可同时实现溶菌酶纤维状聚集体的结构与化学特征的表征。光谱分析结果显示，溶菌酶转化形成的纤维结构主要以平行β折叠为主，几乎不含反平行β折叠。蛋白刚度等特征与所获得的二级结构信息具有良好的相关性，可反映蛋白在纤维化状态下的分子状态。我们将本研究获得的结构与化学细节与透射电子显微镜（transmission electron microscopy，简称TEM）、圆二色光谱（circular dichroism，简称CD）的检测结果进行了对比。本研究利用纳米红外光谱获取红外光谱数据，从形态学、分子结构、二级结构含量、稳定性以及交叉β核心尺寸等多个维度对溶菌酶淀粉样纤维的结构进行了表征。研究表明，纳米红外光谱可作为其他生物物理研究的补充手段用于分析蛋白聚集过程，尤其适用于研究参与聚集过程的蛋白，助力抗淀粉样聚集靶向分子的设计。具体而言，纳米红外光谱可提供高分辨率的信息与特征指纹图谱，用于判定蛋白聚集状态。本文由Ramaswamy H. Sarma转交。