Dissociation equilibrium of human recombinant interferon gamma

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Dynamics

Background:

• Interferon gamma (IFN-γ) is a crucial cytokine involved in immune responses.
• The biologically active form of IFN-γ is a dimer of two 17 kDa polypeptide chains.
• Understanding the structural dynamics of IFN-γ is essential for its function.

Purpose of the Study:

• To investigate the impact of dimer-monomer dissociation on IFN-γ's biophysical properties.
• To determine the thermodynamic and kinetic parameters of the IFN-γ dimer-monomer equilibrium.
• To explore the relationship between monomer formation, aggregation, and functional inactivation.

Main Methods:

• Fluorescence spectroscopy to measure quantum yield and energy transfer.
• Analysis of fluorescence decay and anisotropy decay.
• Application of a theoretical mathematical model for equilibrium analysis.
• Temperature-dependent fluorescence measurements.

Main Results:

• Dimer dissociation into monomers significantly reduced fluorescence quantum yield and Tyr-Trp energy transfer efficiency.
• Monomer formation altered fluorescence decay kinetics and anisotropy decay.
• The dimer-monomer dissociation is an endothermic process favored by low protein concentrations (<1 µM) and higher temperatures.
• Monomerization was accompanied by slow, partially reversible aggregation, leading to IFN-γ inactivation.

Conclusions:

• Monomeric conformers of interferon gamma may be prone to aggregation.
• The structural transition from dimer to monomer impacts IFN-γ's biophysical properties and leads to functional loss.
• Understanding these dynamics is key to maintaining IFN-γ stability and activity.