Structural view of insulin adsorption on the multiple sizes of Cu nanoparticles; molecular dynamics simulation study.

Copper nanoparticles with different sizes cause significant changes in humans, and their interaction with biological molecules such as proteins is one of molecular biology's most critical and difficult challenges. One of the valuable tools for understating the mechanisms of different protein-nanoparticle interactions are molecular dynamics simulations. The present work attempts to understand how insulin interaction mechanisms Cu nanoparticles of different sizes (2, 6, and 10 nm) may occur with the molecular dynamics simulations methods. According to the results, in comparison to 2 and 6 nm nanoparticles, insulin interaction with the Cu 10 nm nanoparticle surface exhibits higher relative stability. The Van der Waals Forces (VDW) interactions show that by increasing the nanoparticle size from 2 nm to 6 nm (-673.32 and -847.83, respectively), the VDW energy leads to a significant increase. Although in the CU 10 nm, a noticeable decrease in VDW energy interaction was demonstrated (-357.21) due to present of three disulfide bond which act as a node that limits the excessive opening of insulin and another reason is the decline of surface electron density with increasing Cu-NP size. The secondary structure changes of insulin in the interaction with different sizes of Cu nanoparticles show the B-chain of insulin in the 2 and 6 nm nanoparticles systems had an essential role in the formation of interaction energy, in return for Cu 10 nm nanoparticle with the lowest energy level the chain-A has the bolder role. In the insulin-Cu 6 nm nanoparticle β-sheet structure formation in the Gln, His, Leu, Gly, Glu, and Arg residues was observed around 30 ns. Also, in these amino acids, a partial β-sheet formation in B-chain has been apparent in the insulin-Cu 2 nm nanoparticle system. In the presence of the largest Cu nanoparticle in this study, a rise in helix, random coil, and B-bridge in secondary insulin structure was seen. It is considerable that in this system the most significant structural change occurring in the A-chain. The results of the hydrophilic-hydrophobicity properties and solvent accessible surface analyses also indicated that the insulin is unfolded during its interaction with different sizes of Cu nanoparticles.