Cobalt probing of structural alternatives for insulin in solution

Area of Science:

• Biochemistry
• Structural Biology
• Protein Chemistry

Background:

• Insulin exists as hexamers with specific T and R conformational states.
• Inorganic anions and phenolic compounds induce transitions between these states.
• Metal ion coordination plays a role in insulin's structural dynamics.

Purpose of the Study:

• To investigate the T-R transition in insulin hexamers.
• To elucidate the role of metal ions in insulin structural transformation.
• To use cobalt insulin as a spectroscopic probe for coordination changes.

Main Methods:

• Spectroscopic analysis (UV-Vis absorption, Circular Dichroism) of insulin.
• Induction of T-R transitions using inorganic anions (SCN-) and cresol.
• Utilizing cobalt (Co2+ and Co3+) and zinc (Zn2+) ions as metal probes.
• Studying metal-free and metal-substituted insulin hexamers.

Main Results:

• Inorganic anions and cresol induce T-R transitions, altering B-chain conformation and metal coordination from octahedral to tetrahedral.
• Cobalt insulin's spectral properties reflect transformation-dependent coordination changes.
• Cresol induces T6-R6 transformation, while SCN- induces T6-T'3R3 transformation.
• Oxidation of Co2+ in insulin affects structure, with Co3+ being more resistant to transformation.

Conclusions:

• Insulin's T-R transition is influenced by both ligands and metal ion coordination.
• Cobalt insulin is a valuable probe for studying these interdependent structural and coordination dynamics.
• Different anions and compounds induce distinct transformation pathways affecting insulin's quaternary structure.