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 β structure with lower-frequency band positions. All protein aggregates acquire this new β band following the aggregation process involving intermolecular interactions. The β sheets in some proteins arise from regions of the polypeptide that are helical or non β 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 β structure. The new β could be most likely attributed to stronger hydrogen bonds in the intermolecular β-sheet structure present in the protein aggregates.