Structure-function relationships in the free insulin monomer

Area of Science:

• Biochemistry
• Protein Chemistry
• Chemical Biology

Background:

• Insulin exists in various associated forms (monomers, dimers, hexamers) in solution.
• Understanding the chemical properties of monomeric insulin is crucial for its function and drug development.

Purpose of the Study:

• To determine the chemical properties of functional groups in free monomeric insulin.
• To compare these properties with those of associated insulin forms.
• To elucidate the structural basis for any observed differences.

Main Methods:

• Chemical property determination of insulin functional groups at 0.5 microM concentration.
• Analysis of reactivity-pH profiles, focusing on ionization states and pKa values.
• Comparison with X-ray crystallographic data of hexameric insulin.

Main Results:

• Glycine N-terminus and tyrosine phenolic groups showed similar properties to associated insulin.
• Lysine epsilon-amino and histidine imidazole groups exhibited significantly altered properties.
• A second ionization (pKa 10.1) was observed for histidine imidazole groups, in addition to the pKa 6.8 ionization.

Conclusions:

• Observed alterations in monomeric insulin are attributed to the disruption of inter-unit interactions present in associated forms.
• The fundamental conformation of the insulin monomer remains consistent across free and associated states in solution.