Solution physicochemical properties of bovine beta 2-microglobulin. Aggregation states

Area of Science:

• Biochemistry
• Protein Chemistry
• Immunology

Background:

• Bovine beta 2-microglobulin (beta 2-m) is the light chain of the histocompatibility antigen.
• Previous studies suggested time-dependent aggregation of bovine beta 2-m in solution.

Purpose of the Study:

• To clarify the molecular states and aggregation behavior of bovine beta 2-m in solution.
• To investigate the influence of concentration, temperature, and pH on its structure and stability.

Main Methods:

• Ultracentrifugation (sedimentation equilibrium and velocity)
• Spectropolarimetry (circular dichroism)

Main Results:

• At low concentrations (<0.3 mg/ml), bovine beta 2-m exists as a compact monomer (Mr = 11,800).
• At higher concentrations (>0.4 mg/ml), reversible monomer-tetramer self-association occurs, favored by lower temperatures.
• Irreversible aggregation and denaturation (increased disordered structure) are temperature-dependent, occurring over 7 days.
• Aggregation rate decreases as pH approaches the isoelectric point (pH 7).

Conclusions:

• Bovine beta 2-m displays concentration-dependent reversible self-association and temperature-dependent irreversible aggregation and denaturation.
• The protein's structural dynamics are sensitive to environmental conditions like pH and temperature.