Binding sites and structure of peptides bound to SiO2 nanoparticles studied by solution NMR spectroscopy

Understanding the mechanism of the interaction between inorganic materials and peptides is important for the development of organic/inorganic hybrid materials. The titanium-binding peptide (TBP; Arg1-Lys2-Leu3-Pro4-Asp5-Ala6) has been reported to possess a high binding affinity to SiO2 as well as TiO2 surfaces. Here, we report the binding modes and mechanism of the TBP to SiO2 nanoparticles. To accomplish this objective, we analyzed the binding sites of the TBP to a SiO2 surface and the structure of the TBP bound to the SiO2 using solution NMR spectroscopy. Saturation transfer difference (STD) NMR analysis was performed to identify the TBP sites that interact with the SiO2 surface, and then Arg1 and Asp5 were identified to be in close contact with the SiO2 surface. The structure of the TBP bound to SiO2 was well defined, and the Arg1 and Asp5 side chains face in the same direction. The combination of these results validates that the guanidyl group of Arg1 and the carboxyl group of Asp5 interact electrostatically with the silanol groups SiO- and SiOH2+ on the SiO2 surface, respectively. The binding mode of TBP/SiO2 was found to be different from that of the TBP/TiO2 system, which has been previously reported.