Post by williamplayer on Jan 15, 2015 15:04:30 GMT
Interlayer Water Regulates the Bio-nano Interface of a β-sheet Protein stacking on Graphene
Using molecular dynamics simulations, we investigated an integrated bio-nano interface consisting of a β-sheet protein stacked onto graphene. We found that the stacking assembly of the model protein on graphene could be controlled by water molecules. The interlayer water filled within interstices of the bio-nano interface could suppress the molecular vibration of surface groups on protein, and could impair the CH···π interaction driving the attraction of the protein and graphene. The intermolecular coupling of interlayer water would be relaxed by the relative motion of protein upon graphene due to the interaction between water and protein surface. This effect reduced the hindrance of the interlayer water against the assembly of protein on graphene, resulting an appropriate adsorption status of protein on graphene with a deep free energy trap. Thereby, the confinement and the relative sliding between protein and graphene, the coupling of protein and water, and the interaction between graphene and water all have involved in the modulation of behaviors of water molecules within the bio-nano interface, governing the hindrance of interlayer water against the protein assembly on hydrophobic graphene. These results provide a deep insight into the fundamental mechanism of protein adsorption onto graphene surface in water.
Introduction
Bio-nanotechnology has advanced to the point at which it can now focus on understanding and controlling bio-nano interface interactions. The basic biomolecule and the star nanomaterial, protein and graphene, play significant roles in the revolution of science and industry. The bio-nano interface between a protein and graphene has attracted broad interest for the development of biocompatible hybrid materials, nanomedicines, biomimetic sensors, and protein separation and purification strategies. Because water is the universal solvent in biological systems, it is involved in the formation of bio-nano interfaces. Understanding the interactions between a protein and graphene in a water environment is fundamental to our ability to regulate protein and graphene interactions.
Investigations on protein-nanomaterial interfaces in aqueous solutions have progressed from the colloidal scale to the molecular level. Water has been found to actively participate in the assembly of proteins on a solid surface by mediating interactions between binding partners and protein conformations. Based on molecular dynamics (MD) simulations and statistical analyses, it has recently been proposed that the orientations and ordering of water layers adjacent to an uncharged solid surface dictate the mechanism of adsorption for a protein onto an uncharged solid. Near the surface of graphene, hydrophobic hydration results in hydrogen bond (HB) fluctuations, density oscillations and dipole biasing of water molecules. Non-covalent interactions (NCIs), such as van der Waals (vdW) and π-π stacking between proteins and graphene as well as heterogeneous and dynamic hydration environments impact the assembly of proteins on graphene; e.g. the α-helix structure of a peptide on a dry graphene surface can transform into a distorted helical structure in the presence of water. In addition, the flexibility of a graphene monolayer has been shown to be important for the adsorption of small peptides and for the depletion of water interlayer. Understanding the interactions between protein, water and graphene is a key to controlling their behaviors within bio-nano interfaces. Unfortunately, the interactions within a water-regulated protein-graphene (P-G) interface, particularly the molecular behavior of water within the assembled interface between a bulk protein and graphene, have not yet been well characterized.
READ FULL ARTICLE: www.nature.com/srep/2015/150105/srep07572/pdf/srep07572.pdf
Using molecular dynamics simulations, we investigated an integrated bio-nano interface consisting of a β-sheet protein stacked onto graphene. We found that the stacking assembly of the model protein on graphene could be controlled by water molecules. The interlayer water filled within interstices of the bio-nano interface could suppress the molecular vibration of surface groups on protein, and could impair the CH···π interaction driving the attraction of the protein and graphene. The intermolecular coupling of interlayer water would be relaxed by the relative motion of protein upon graphene due to the interaction between water and protein surface. This effect reduced the hindrance of the interlayer water against the assembly of protein on graphene, resulting an appropriate adsorption status of protein on graphene with a deep free energy trap. Thereby, the confinement and the relative sliding between protein and graphene, the coupling of protein and water, and the interaction between graphene and water all have involved in the modulation of behaviors of water molecules within the bio-nano interface, governing the hindrance of interlayer water against the protein assembly on hydrophobic graphene. These results provide a deep insight into the fundamental mechanism of protein adsorption onto graphene surface in water.
Introduction
Bio-nanotechnology has advanced to the point at which it can now focus on understanding and controlling bio-nano interface interactions. The basic biomolecule and the star nanomaterial, protein and graphene, play significant roles in the revolution of science and industry. The bio-nano interface between a protein and graphene has attracted broad interest for the development of biocompatible hybrid materials, nanomedicines, biomimetic sensors, and protein separation and purification strategies. Because water is the universal solvent in biological systems, it is involved in the formation of bio-nano interfaces. Understanding the interactions between a protein and graphene in a water environment is fundamental to our ability to regulate protein and graphene interactions.
Investigations on protein-nanomaterial interfaces in aqueous solutions have progressed from the colloidal scale to the molecular level. Water has been found to actively participate in the assembly of proteins on a solid surface by mediating interactions between binding partners and protein conformations. Based on molecular dynamics (MD) simulations and statistical analyses, it has recently been proposed that the orientations and ordering of water layers adjacent to an uncharged solid surface dictate the mechanism of adsorption for a protein onto an uncharged solid. Near the surface of graphene, hydrophobic hydration results in hydrogen bond (HB) fluctuations, density oscillations and dipole biasing of water molecules. Non-covalent interactions (NCIs), such as van der Waals (vdW) and π-π stacking between proteins and graphene as well as heterogeneous and dynamic hydration environments impact the assembly of proteins on graphene; e.g. the α-helix structure of a peptide on a dry graphene surface can transform into a distorted helical structure in the presence of water. In addition, the flexibility of a graphene monolayer has been shown to be important for the adsorption of small peptides and for the depletion of water interlayer. Understanding the interactions between protein, water and graphene is a key to controlling their behaviors within bio-nano interfaces. Unfortunately, the interactions within a water-regulated protein-graphene (P-G) interface, particularly the molecular behavior of water within the assembled interface between a bulk protein and graphene, have not yet been well characterized.
READ FULL ARTICLE: www.nature.com/srep/2015/150105/srep07572/pdf/srep07572.pdf