R6 hexameric insulin complexed with m-cresol or resorcinol

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• Human insulin exists in hexameric forms, crucial for storage and release.
• Understanding insulin structure is key to developing improved therapeutic formulations.

Purpose of the Study:

• To elucidate the structural basis of R(6) human insulin hexamers.
• To identify binding sites for phenolic derivatives and their interactions.
• To investigate the conformational changes associated with insulin's T to R transition.

Main Methods:

• X-ray crystallography was employed to determine the structures of three R(6) human insulin hexamer crystal forms.
• High-resolution diffraction data (1.78-1.9 Å) were collected and structures were refined.
• Analysis of atomic interactions and conformational differences between hexamer states.

Main Results:

• Three R(6) human insulin hexamer structures (monoclinic and rhombohedral) were determined at high resolution.
• Phenolic derivatives were consistently found bound at a specific phenolic site, forming hydrogen bonds with CysA6 and CysA11.
• Additional binding sites for phenolic derivatives were identified within or between hexamers.
• Minor structural variations were observed, including sodium ion coordination affecting B chain N-termini and packing differences.
• Conformational changes in GluB13 side chains correlated with the T to R conformational transition.

Conclusions:

• The R(6) human insulin hexamer structure is well-defined, with phenolic derivatives occupying specific binding pockets.
• Phenolic binding appears to stabilize the R(6) state.
• The deprotonation of GluB13 side chains is linked to the T to R conformational transition, providing insights into insulin's allosteric regulation.