Label-Free Detection of β-Sheet Polymorphism.

Area of Science:

• Biophysics
• Spectroscopy
• Materials Science

Background:

• Characterizing diverse secondary structures in peptide and protein aggregates is vital for understanding amyloidogenic diseases and developing new biomaterials.
• Current methods often struggle to differentiate multiple structural polymorphs within a single aggregate.
• Distinguishing these structures is key for therapeutic strategies and advanced material design.

Purpose of the Study:

• To develop and demonstrate a label-free spectroscopic technique for identifying multiple beta-sheet configurations within individual peptide aggregates.
• To utilize two-dimensional infrared (2D IR) spectroscopy and transition dipole strength (TDS) analysis for enhanced structural sensitivity.
• To reveal structural heterogeneity in peptide aggregates previously considered homogeneous.

Main Methods:

• Employing two-dimensional infrared (2D IR) spectroscopy to analyze peptide aggregates.
• Calculating transition dipole strength (TDS) spectra from the ratio of linear and 2D signals.
• Analyzing TDS spectra to identify distinct beta-sheet structures and their couplings.

Main Results:

• The TDS spectra successfully distinguished two distinct beta-sheet structures within AcKFE8 peptide aggregate fibers, which appeared homogeneous by other methods.
• Early-stage aggregation revealed additional peaks in TDS spectra, suggesting the presence of weakly coupled beta-sheet structures.
• The method demonstrated high sensitivity to vibrational coupling, providing detailed protein structure information.

Conclusions:

• This novel 2D IR spectroscopy method offers a powerful, label-free approach to differentiate multiple oligomeric and polymorphic structures in peptide aggregates.
• The technique provides insights into the heterogeneity of protein aggregation processes.
• This method has significant implications for the study of amyloid diseases and the design of novel protein-based biomaterials.