Living systems utilize macromolecular-inorganic hybrid structures to create biomaterials with outstanding properties. Precise programming of the protein-inorganic interface is crucial to the development of such materials. Hence, understanding the mechanism by which the protein matrix assembles and using that understanding to mimic the structure of protein matrices at the crystal-solvent interface would enable the creation of materials with precise control over the morphology and spatial arrangement of the subunits. In this work, protein nanorods exhibiting an arrangement of amino acid sidechains lattice-matched to the cation sublattice on muscovite mica (001) were designed using Rosetta, and their self-assembly was studied by high speed in situ AFM for a range of electrolyte types and concentrations. Our results show that the proteins formed 2D liquid crystal (LC) phases. Moreover, for KCl concentrations above 1 M, a 2D smectic phase with long-range order was achieved. The results also show that protein mobility increases dramatically with KCL concentration, thus promoting the formation of ordered LC phases. The known effects of high salt concentration on both charge screening and the structure of the interfacial hydration layers likely play decisive roles in achieving order. When muscovite, which possesses buried hydroxyl groups that break the 3-fold symmetry, was replaced with phlogopite, which has an identical cation sublattice but exhibits true 3-fold symmetry, the smectic phase was lost and the protein rods assembled into an isotropic phase with domains equally aligned along the three equivalent directions. By comparing our experimental results with Monte Carlo simulations, we find that assembly is primarily driven by entropic effects, while orientation selection is controlled by the arrangement of the cation sub-lattice, biased by the alignment of the hydroxyl groups.

Formation of 2D liquid crystal phases by <i>de novo</i> designed proteins at crystal-solution interfaces

2019 Fall National Meeting

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Formation of 2D liquid crystal phases by de novo designed proteins at crystal-solution interfaces