Allosteric Residue Dynamics in Insulin: Temperature Induces Shift from Dihexamer to Hexamer Collective Motion

Structures using X-ray diffraction data collected to 2.3 Å, 2.85 Å, and 2.88 Å resolutions have been determined for the long-acting dihexamer insulin at three different temperatures ranging from 100°K to 300°K. It is determined that the unit-cell value of insulin crystal at 100°K temperature has changed at 200°K temperature. This change might be due primarily to subtle repacking of the molecule and loss of noncovalent interactions of myristic acid that binds two hexamers, exhibiting the largest movements. Computational analyses show that allosteric residues and fatty-acid binding residue of insulin hexamers display reduced overall collectivity and inter-residue coupling, likely arising from crystal mosaicity increase and structural fluctuations through elevated thermal motion. This breakpoint has been observed at a characteristic temperature of 200°K, perhaps emphasizing underlying alterations in the dynamic structure of the fatty acid-solvent interface in dimer of hexamer. Combined with computational analysis, findings reveal key insights into thermal stability mechanisms crucial for developing thermostable insulin formulations in industrial applications.