Recognition, Adsorption And Stability Of Proteins Adsorbed On Different Kinds Of Surfaces

Protein is one of the most important components of organism and it almost participates in all the life process and cell activity. The interaction of protein and interface plays important role in many fields, such as the copy of genetic material, the expression of gene regulation, cell metabolism, cell signal transduction, the short-range and long-range communications between cells and cells, organism morphogenesis, cell adhesion, regulation of the crystal growth. The transport and storage of proteins, cell adhesion and regulation of the crystal growth were carried out by the interaction of protein and biomaterials. And the processes of enzyme catalysis, immune response and signal transduction must depend on the protein-protein interaction. Because of the high surface activity, protein could be adsorbed on the solid surface from the solution. And this adsorption phenomenon was popular in the fields of medicine, engineering and technology. Many studies in the past have confirmed the observation that the proteins are adsorbed onto the implanted surface from the bodily fluids before osteoblasts were adhered. When blood contact with the implanted materials, it could cause the blood coagulation and immune response. And the yield would be reduced by the biological pollution, which was caused by the protein adsorption on the engineering reactor surface. It was found that there would be many kinds of interactions between protein and other materials during process of protein adsorption onto the solid surface, such as protein-protein interaction, protein-water interaction and protein-interface interaction. These interactions were composed of hydrophobic interaction, electrostatic interaction, VDW interaction and hydrogen bond etc. All these kinds of interaction would affect the structure of proteins, and the bioactive activity of proteins would also be changed or weakened.In this paper, molecular mechanism and quantum mechanism were combined to study the interaction between protein and different kinds of nanoscale interfaces. Water, the regular inorganic crystal and protein molecule was used as the interface to research the adsorption, recognition and stability of proteins adsorption on these kinds of surfaces. Firstly, molecular dynamics (MD) simulation was used to optimize the geometry of protein and to achieve the equilibrium state of the protein-interface system. Then the steered molecular dynamics (SMD) simulation was carried out to analyze the dynamic characters of the protein-interface interaction. And the quantitative calculation was also employed to validate the interaction mechanism by studying the key interaction groups. In this way, the key interaction site and the interaction mode could be found and these findings could be applied in the fields of drug design, biomaterials, the separation and purification of protein, and biomineralization. The major contributions of this work are as follows:1. The stability of HIVp with the external disturbance in water molecules was studied via MD, SMD and domain analysis. It was found that the two long peptide chains of HIVp, which own the same amino acid sequence, had the similar motion mode. It was also found that the force endurance of HIVp is anisotropic and the active site could be destroyed by the external force most easily. HIVp could be disturbed more easily with the increase of pushing force, however, at the beginning it can resist against the disturbance for some times. It could be distinctly found from domain analysis that a shell-broken motion mode was happened during the disturbance process. The research on the motion mode of HIVp suggests that HIVp has a self-protection function and the outside region of HIVp can resist against the external disturbance and deform sacrificially to avoid denaturation of the whole protein.2. The adsorption-desorption behavior of leucine-rich amelogenin protein (LRAP) on the hydroxyapatite [HAP] (001) surface was studied in detail. Six different orientations of LRAP were chose to be put on a fixed HAP (001) surface and the degrees of protein adsorption/desorption on HAP surface in the six systems were analyzed. It was found that the electrostatic interaction contributed mainly to the adsorption of LRAP on the HAP (001) surface. Moreover, it was found that the-COOˉclaw of LRAP grasps the calcium ion with its two oxygen atoms in a special triangle form. This interaction form can resist external forces and is the key factor of the adsorption between LRAP and HAP.3. The adsorption-desorption behaviors of LRAP on a series of SiHA (100) surfaces were investigated to study the effect of silicate substitution. HAP (100) crystal surface, which takes PO43- anions in the outmost layer, was convenient for the substitution of PO43- by SiO44-. It was found that the surface-substituted silicate causes a shield effect, which could weaken the electrostatic interaction between LRAP and SiHA. The shield effect is composed of the charge repulsion effect of the excessive negative charge of SiO44- and the steric hindrance effect of SiO44-. It was also found that there is a certain appropriate substitution scale of silicate. If the incorporation of silicate were too little, silicate would not behave its shield effect obviously. Whereas superfluous silicate would decrease the interaction of LRAP with HAP and thus the graduating function of LRAP would be diminished.4. Site-directed mutagenesis method was employed to study the interaction between insulin-like growth factor-Ⅰ(IGF-I) and insulin-like growth factor binding protein-4 (IGFBP4). It was found that the key adsorption region of IGF-I was a short fragment of polypeptide chain, which was composed of 7 sequential amino acids, and it existed in the shape of a ring. The key adsorption residues were mutated respectively to analyze the interaction contribution of each residue. And it was distinctly found that residue Asp38 of IGF-I was the most important adsorption site. It was also found that hydrogen bond and the large embedded area contributed mostly to the strong combination of IGF-I and IGFBP4.