Distinct β-Sheet Structure in Protein Aggregates Determined by ATR-FTIR Spectroscopy

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the conformation of aggregated proteins in vivo and in vitro. Several different protein aggregates, including amyloid fibrils from several peptides and polypeptides, inclusion bodies, folding aggregates, soluble oligomers, and protein extracts from stressed cells, were examined in this study. All protein aggregates demonstrate a characteristic new beta structure with lower-frequency band positions. All protein aggregates acquire this new beta band following the aggregation process involving intermolecular interactions. The beta sheets in some proteins arise from regions of the polypeptide that are helical or non beta in the native conformation. For a given protein, all types of the aggregates (e.g., inclusion bodies, folding aggregates, and thermal aggregates) showed similar spectra, indicating that they arose from a common partially folded species. All of the aggregates have some nativelike secondary structure and nonperiodic structure as well as the specific new beta structure. The new beta could be most likely attributed to stronger hydrogen bonds in the intermolecular beta-sheet structure present in the protein aggregates.