YB-1 AP-CSD Forms Cross-β Amyloid Fibrils Without Secondary-Structure Conversion In Vitro

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Y-box binding protein 1 (YB-1) is crucial for messenger ribonucleoprotein particle (mRNP) metabolism and stress granule formation.
• YB-1 self-assembly into fibrils is primarily linked to its cold shock domain (CSD).

Purpose of the Study:

• To investigate the fibrillization process of the YB-1 fragment spanning residues 1-129 (AP-CSD).
• To elucidate the structural characteristics and kinetics of AP-CSD fibril formation.

Main Methods:

• Far-UV circular dichroism (CD) spectroscopy
• Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR)
• Proton nuclear magnetic resonance (1H NMR) spectroscopy
• Oriented fiber X-ray diffraction

Main Results:

• AP-CSD forms amyloid fibrils under physiological ionic strength (0.12-0.15 M KCl) over 45-50 hours with linear growth.
• Secondary structure remains largely unchanged during aggregation, as shown by CD and ATR-FTIR.
• NMR confirms depletion of soluble species, and X-ray diffraction reveals cross-β structure.

Conclusions:

• The slow fibrillization kinetics suggest an activation barrier involving early association events rather than global refolding.
• Preservation of native-like fold during cross-β structure formation may enable YB-1 assemblies to evade cellular quality control.
• This mechanism provides a framework for YB-1 assembly persistence under cellular stress and during aging-related proteostasis decline.