Amyloid Formation of Stefin B Protein Studied by Infrared Spectroscopy

Background: Stefin B, an established model protein for studying the stability and mechanism of protein folding, was used for monitoring protein aggregation and formation of amyloid structure by infrared spectroscopy. Methods: The analyses of the integral intensities of the low frequency part of the Amide I band, which is directly connected to the appearance of the cross-beta structure reveals the temperature but not pH dependence of stefin B structure. Results: We show that pH value has significant role in the monomer stability of stefin B. Protein is less stable in acidic environment and becomes more stable in neutral or basic conditions. While in the case of the Amide I band area analysis we apply only spectral regions characteristic for only part of the protein in cross-beta structure, the temperature study using multivariate curve resolution (MCR) analysis contains also information about the protein conformation states which do not correspond to native protein nor protein in cross-beta structure. Conclusions: These facts results in the slightly different shapes of fitted sigmoid functions fitted to the weighted amount of the second basic spectrum (sc2), which is the closed approximation of the protein spectra with cross-beta structure. Nevertheless, the applied method detects the initial change of the protein structure. Upon the analysis of infrared data a model for stefin B aggregation is proposed.

Automated summary

This study used Stefin B as a model protein to monitor protein aggregation and amyloid structure formation using infrared spectroscopy. The results showed that pH value significantly affects the monomer stability of Stefin B, with lower stability in acidic environment and higher stability in neutral or alkaline conditions. The proposed infrared data model provides insights into the aggregation process of Stefin B.