Conformational dynamics of insulin in solution. Circular dichroic studies

Area of Science:

• Biochemistry
• Structural Biology
• Protein Chemistry

Background:

• Insulin's biological activity is linked to its conformational state.
• Understanding insulin's structure in solution is key to its mechanism of action.

Purpose of the Study:

• To investigate the conformational changes of bovine insulin in solution.
• To determine the effects of concentration and pH on insulin's conformation.
• To characterize the monomeric state of insulin.

Main Methods:

• Circular dichroic (CD) spectroscopy was used to study insulin's conformation.
• Concentration-dependent and pH-dependent CD spectra were analyzed.
• A nonlinear least-squares iterative computer program was employed for data analysis.
• Mean residue ellipticities were extrapolated to calculate monomeric and dimeric conformations.

Main Results:

• Insulin exhibits two major conformational states: conformation I (monomeric, dilute solutions) and conformation II (crystalline, associated states).
• Conformation I has 21% less helix content than conformation II.
• The conformational transition is of the helix-coil type.
• Changes in CD spectra with pH closely correspond to changes in sedimentation coefficients.

Conclusions:

• Bovine insulin undergoes significant conformational transitions induced by concentration and pH.
• Conformation I, predominant in monomeric insulin, differs substantially from the crystalline form.
• This study provides the first report on conformational studies of insulin in its biologically active monomeric state.
• Understanding these conformational changes is vital for deciphering the molecular basis of insulin action.