Conformational Flexibilities and Solvation Properties of Insulin in Aromatic Amino Acid Solutions: A Molecular Dynamics Study Using CHARMM Drude Polarizable Model

Abstract

Aromatic amino acids (AAA) play a crucial role in the structure and function of proteins. A higher level of AAA causes several diseases, controls insulin levels. In this work, we carried out atomistic molecular dynamics simulations by using CHARMM Drude polarizable force field to investigate the conformational properties of insulin monomer in 2M phe, tyr, trp solutions as well as in pure aqueous solution to compare the relative changes of protein conformations, its solvation properties and the interactions of the free AAA with insulin. Although insulin’s native folded form was intact in all the solutions within the simulation length scale, we observed that the protein is a little more flexible and less compact in phe solution than in tyr/trp solutions. The free AAAs identified to self-aggregate around the protein surface and form clusters of different sizes. They interacted with insulin, significantly through cation/anion–[Formula: see text] and [Formula: see text]–[Formula: see text] stacking, and partly through hydrogen bonded interactions. Among the three, trp was prone to interact through cation–[Formula: see text] interactions while phe and tyr interacted through [Formula: see text]–[Formula: see text] stacking with insulin. Despite a significant number of free AAA molecules in the solvation shell, insulin was observed to be sufficiently hydrated and formed hydrogen bonds with water. Some of our findings agreed with the available experimental results that establish the reliability of the chosen force field. Our findings would interpret the interactions between the free AAA and insulin in solution, helpful to recognize the microscopic details of AAA governed biological processes in living organisms.