Characterizing polyproline II conformational change of collagen superhelix unit on adsorption on gold surface.

The dynamic process of protein binding onto a metal surface is a frequent occurrence as gold nanoparticles are increasingly being used in biomedical applications, including wound treatment and drug transport. Collagen, as a major component of the extracellular matrix, has potentially advantageous biomedical applications, due to its excellent biocompatibility and elasticity properties. Therefore, a mechanistic comprehension of how and which species in collagen interact with gold nanoparticles is a prerequisite for collagen-gold complexes in clinical application. However, the dynamic behavior of collagen with the polyproline II (PPII) conformation on gold sheets at the molecular level is too complex to capture under current experimental conditions. Here, using molecular dynamics simulations, we investigate the adsorption process and conformational behavior of the tripeptide Gly-Pro-Hyp with the repetitive unit of the collagen superhelix on the gold surface as a function of number of repeating units from 1 to 10. The different numbers of repeating units all prefer to approach the gold surface and adsorb charged residues at the C-terminal or N-terminal ends, tending to form arch structures on the gold surface. Compared with the various tripeptide units in solution still retaining the native PPII conformation, the presence of the gold surface affects the formation of hydrogen bonds between the protein and water molecules, thus disrupting the PPII conformation of collagen. Specifically, the interaction between the gold surface and HYP limits the rotation of the dihedral angle of collagen, resulting in a tendency for the PPII conformation of the gold surface to transform to the β-sheet conformation. The results provide an indication of how to improve the interaction between the terminal groups and the gold surface for the design of a bioavailable protein-gold material for medicinal purposes.