PNNL

Abstract

The adsorption of proteins at solid–liquid interfaces is important in a number of biomedical applications as well as for efforts to design and synthesize hierarchically organized materials using protein assembly at interfaces. Yet, the underlying mechanisms governing the adsorption of protein assemblies at surfaces are insufficiently understood. In this study, we explore the interfacial behavior of de novo designed proteins that self-assemble into fibrillar structures with three distinct morphologies—small (S), large (L), and helical (H). Our results show that the S-fibers are metastable relative to the L- and H-fibers, appearing first, but decreasing in number and length as the other fiber-types form and deposit. Our findings also demonstrate that the deposition of these assemblies and their monomeric units onto muscovite mica surfaces is dependent on both the fiber morphology and the solvent environment, which is in turn shaped by the substrate. Notably, the anisotropic surface features of the fiber types — the flat axis of the S- and L-fibers and the helical groove of the H-fibers — are directly correlated with the crystallographic direction along with the fibers align in the mica surface. The direction of alignment, and therefore the orientation along with the energy is minimized, is along the unique axis of the muscovite mica (001) lattice for S- and L-fibers. In contrast, the direction of the substrate-facing groove of the H-fiber helix, preferentially aligns along the remaining two symmetry directions of the muscovite mica (001) lattice. The increase of KCl concentrations to M levels leads to changes in the adsorption behavior of the protein monomers and the fibers, with monomer coverage decreasing relative to the fiber coverage. We discuss these results in light of the understanding of mica-water interfacial structure and its impact of protein adsorption. This work reveals the complex interplay between protein topography, surface structure, and interfacial solvent environment in controlling protein adsorption at solid–liquid interfaces.