Solid-State NMR and MD Study of the Structure of the Statherin Mutant SNa15 on Mineral Surfaces

Elucidation of the structure and interactions of proteins at native mineral interfaces is key to understanding how biological systems regulate the formation of hard tissue structures. In addition, understanding how these same proteins interact with non-native mineral surfaces has important implications for the design of medical and dental implants, chromatographic supports, diagnostic tools, and a host of other applications. Here, we combine solid-state NMR spectroscopy, isotherm measurements, and molecular dynamics simulations to study how SNa15, a peptide derived from the hydroxyapatite (HAP) recognition domain of the biomineralization protein statherin, interacts with HAP, silica (SiO₂), and titania (TiO₂) mineral surfaces. Adsorption isotherms are used to characterize the binding affinity of SNa15 to HAP, SiO₂, and TiO₂. We also apply 1D ¹³C CP MAS, 1D ¹⁵N CP MAS, and 2D ¹³C-¹³C DARR experiments to SNa15 samples with uniformly ¹³C- and ¹⁵N-enriched residues to determine backbone and side-chain chemical shifts. Different computational tools, namely TALOS-N and molecular dynamics simulations, are used to deduce secondary structure from backbone and side-chain chemical shift data. Our results show that SNa15 adopts an α-helical conformation when adsorbed to HAP and TiO₂, but the helix largely unravels upon adsorption to SiO₂. Interactions with HAP are mediated in general by acidic and some basic amino acids, although the specific amino acids involved in direct surface interaction vary with surface. The integrated experimental and computational approach used in this study is able to provide high-resolution insights into adsorption of proteins on interfaces.