Abstact

The morphologies of dry MrgA protein monolayers on different solid substrates prepared by a three-step procedure (adsorption from an incubation solution, rinsing to remove excess salt and protein, and drying) were investigated using atomic force microscopy. MrgA is a dodecameric iron-storage protein which can form hexagonal, two-dimensional (2D) crystalline monolayers on hydrophilic surfaces at low supersaturation. The formation of such two-dimensional crystals is heavily dependent on the pH and the salinity of the incubation solution as well as on the surface properties. Correlation of surface coverage with substrate charge, ionic strength, and pH indicates the dominance of electrostatic effects in adsorption, with the balance shifting between intermolecular repulsion and protein-substrate attraction. Close to the isoelectric point (pI) of MrgA, adsorption to the surface and the formation of 2D crystals are favored. By preparation of self-assembled monolayers of thiols with different end groups on template-stripped gold, the surface properties can be varied easily from high to very low protein affinity. The resulting patterns of the crystalline protein structures are novel and could be a starting point for further scientific study, e.g., solid-supported cocrystallization with DNA, and indeed developments with technological applications, such as mesostructured deposition of MrgA-caged nanoparticles.