Interactions at the interface between proteins and minerals

Abstract

Interactions at the interfaces between proteins and minerals drive both protein binding onto the surface of minerals and mineral formation on the surface of proteins. Understanding these interactions is fundamental to the rational design of self-assembling hierarchical structures. De novo designed proteins enable the precise placement of chemical functional groups in three-dimensional space and are thus ideal for investigating organic-mineral interactions. This research has been targeted to address both protein assembly and mineral formation. We investigated the role of charge patchiness in proteins that drive the formation of mineral crystals from precursors in solution. By designing charged template proteins, we gain insight into the assembly mechanisms of titanium oxides from titanium(IV) bis(ammonium lactate)dihydroxide (TiBALDH), where surface-displayed carboxyl and amine groups direct nucleation at room temperature, demonstrating sequence-driven control over titania nucleation phase and spatial organization using homo-oligomeric protein assemblies with D3 symmetry. We characterized the formation and growth of titanium dioxide as directed by the surface charge of various protein assemblies and developed the design principle that alternating positive and negative regions is optimal for forming titanium dioxide. Our research demonstrates that the precise control over functional group placement available to de novo designed proteins enables access to novel assemblies and can influence the crystallinity and morphology of mineral formation. We also employed machine learning and conventional analysis of high-speed atomic force microscopy data to better describe the assembly process of protein nanorods into a liquid crystal arrangement on the surface of mica and the interactions and solution conditions required for that liquid crystal to form. The symmetry of the mineral substrate and the resultant solution structure at the mineral surface influences the symmetry of the protein assembly. The designed interface of the protein allows access to an ordered assembly at the surface. These findings highlight the potential of de novo designed proteins to serve as precise scaffolds for controlling mineral nucleation and assembly, paving the way for the development of tailored bioinspired materials with tunable properties.