Cross-α/β polymorphism of PSMα3 fibrils.

Area of Science:

• Biophysics
• Biochemistry
• Spectroscopy

Background:

• Ordered protein aggregates, particularly cross-β amyloid fibrils, are implicated in numerous human diseases.
• The recent discovery of cross-α amyloid structures presents novel challenges for detection and characterization.
• Phenol soluble modulins (PSMs), like PSMα3, are crucial for *Staphylococcus aureus* biofilm formation and stabilization.

Purpose of the Study:

• To investigate the aggregation process and structural characteristics of phenol soluble modulin alpha 3 (PSMα3) using advanced spectroscopic techniques.
• To differentiate and identify the presence of cross-α and cross-β amyloid polymorphs in PSMα3 fibrils.
• To develop sensitive detection methods for PSMα3 fibrils, addressing a critical need in understanding *Staphylococcus aureus* pathogenesis.

Main Methods:

• Fourier transform infrared (FTIR) spectroscopy was employed to analyze the secondary structure of PSMα3 aggregates.
• Two-dimensional infrared (2D IR) spectroscopy was utilized for a more detailed investigation of fibril structure and dynamics.
• Spectroscopic simulations were performed to aid in the interpretation of experimental data.

Main Results:

• Experimental data revealed the co-existence of both cross-α and cross-β amyloid polymorphs within PSMα3 fibril samples.
• A novel spectroscopic feature specifically indicative of the cross-α fibril structure was identified.
• The study successfully monitored the aggregation of the PSMα3 peptide.

Conclusions:

• PSMα3 fibrils can adopt both cross-α and cross-β secondary structures, highlighting the structural diversity of amyloid formation.
• The newly identified spectroscopic signature provides a valuable tool for detecting and characterizing cross-α amyloid structures.
• These findings advance the understanding of PSMα3 aggregation and have implications for combating *Staphylococcus aureus* infections.