The Anisotropic Adsorption of De Novo Allosteric Two‐Component Protein Fibers on Mica Surfaces

Abstract Protein adsorption at solid–liquid interfaces underlies many biomedical and materials applications, yet the mechanisms governing adsorption of proteins and their assemblies remain poorly understood. Here we investigate de novo–designed proteins that self‐assemble into three fibrillar morphologies — small (S), large (L), and helical (H)—on muscovite mica. S‐fibers are metastable, forming first but diminishing as L‐ and H‐fibers develop and deposit. Adsorption of both fibers and monomers depends on fiber morphology and solvent environment, which is modulated by the substrate. The anisotropic surface features of the fiber types—long axis of S‐ and L‐fibers and helical grooves of H‐fibers—correlate with specific crystallographic directions on mica (001). S‐ and L‐fibers align along the unique lattice axis, while the substrate‐facing groove of H‐fibers preferentially aligns along the remaining symmetry‐related directions. Increasing potassium chloride (KCl) concentrations to molar levels alters adsorption, decreasing monomer coverage relative to fibers. These observations, interpreted through the effect of interfacial interface, indicate that ion‐mediated modulation of hydration layers governs electrostatic interactions and alignment. This study reveals how coupling between protein topography, substrate crystallography, and hydration structure dictates selective adsorption and orientation of protein assemblies, offering insights for rational biomolecular material design.