HMGB1 B-Box Domain Associates Promote Protein-Polyelectrolyte Interactions

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• High mobility group box 1 (HMGB1) is a nuclear protein acting as an extracellular alarmin.
• HMGB1 signaling can drive inflammation, which is modulated by polyanion binding.
• HMGB1 undergoes phase separation, linked to its function, potentially involving its B-box domain.

Purpose of the Study:

• Investigate the role of the HMGB1 B-box domain in protein self-association.
• Determine how HMGB1 self-association affects its interaction with heparin.
• Elucidate the structural mechanisms underlying HMGB1-heparin interactions.

Main Methods:

• Protein self-association analysis of the HMGB1 B-box domain.
• Electron Paramagnetic Resonance (EPR) spectroscopy to study protein-heparin interactions.
• AlphaFold modeling to predict structural changes and charge distribution.

Main Results:

• The HMGB1 B-box domain forms stable 30 nm self-associates.
• Protein associates significantly enhance heparin binding compared to individual chains.
• AlphaFold modeling revealed that multimerization creates an extended positive charge region enhancing polyanion binding.

Conclusions:

• HMGB1 self-association, mediated by the B-box domain, is critical for enhanced heparin binding.
• Multimerization-induced charge redistribution explains increased affinity for polyanions like heparin.
• These findings provide structural insights into HMGB1's role in immune modulation and phase separation.