Correlating Solid-Binding Peptide Structure with Biomimetic Function

While much progress has been made in elucidating the mode of action of biomineralizing proteins and in emulating their function using combinatorially selected solid-binding peptides (SBPs), we remain far from duplicating the sophisticated architectures produced by biological systems. This is in part due to a poor understanding of the relationship between SBP conformation and inorganic adhesion and precipitation. Here, we focus on correlating the structure of Car9, a SiO₂/TiO₂-binding dodecapeptide originally isolated for its ability to recognize the edges of graphitic nanostructures, with silica binding affinity and titania precipitation. Starting with Rosetta and molecular dynamics predictions of the solution and silica-bound structures of Car9, we systematically mutagenize key functional and structural residues, predict the conformation of the mutants, produce them as GFP fusions, quantify the binding of the resulting panel of variants to SiO₂ via SPR and pull-down experiments, and characterize the influence of mutations on TiO₂ mineralization using fluorescence spectroscopy, Ti-depletion, TGA and SEM experiments. We find that the conformational context in which lysine residues are presented to the solvent plays a crucial role in binding and mineralization and that the impact of lysine substitutions can be mitigated through structural rearrangements that reposition basic residues. More broadly, our results suggest that computational predictions of SBP structures can be used to predict subtle changes in binding and mineralization outcomes.