Deciphering Amyloid Fibril Formation through Protein Concentration by Optical Trapping

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Amyloid fibril formation is implicated in various diseases.
• Understanding the early stages of protein aggregation is crucial for therapeutic development.
• Apoferritin (Fer8) serves as a model protein for studying amyloidogenesis.

Purpose of the Study:

• To investigate the real-time dynamics of protein concentration during amyloid fibril formation.
• To explore the influence of pH (pD) on apoferritin condensation and fibril elongation.
• To elucidate the role of optical trapping in dissecting early-stage amyloidogenesis.

Main Methods:

• Utilized optical trapping combined with time-lapse transmission and fluorescence imaging.
• Observed apoferritin (Fer8) condensation and growth at the laser focus.
• Analyzed protein concentration dynamics and secondary structure changes at different pH (pD) conditions.

Main Results:

• Apoferritin condensates formed within 30 min, reaching ~1.2 μm diameter.
• Initial trapping efficiency varied with pD, being higher at pD 8.4.
• Acidic conditions (pD 1.5, 2.0) showed a delayed but significant second-phase concentration increase.
• A critical concentration (0.53-0.63 mM) was identified for rapid ThT fluorescence onset.
• Optical trapping suggested specific molecular alignment beyond simple concentration effects.

Conclusions:

• Optical trapping is a powerful tool for real-time observation of protein aggregation dynamics.
• pH significantly impacts apoferritin condensation, concentration, and amyloid fibril elongation rates.
• Findings provide insights into the pD-dependent interplay of protein structure, nucleation, and elongation in early amyloid formation.