Fibronectin module FN^III9 adsorption at contrasting solid model surfaces studied by atomistic molecular dynamics

The mechanism of human fibronectin adhesion synergy region (known as integrin binding region) in repeat 9 (FN^III9) domain adsorption at pH 7 onto various and contrasting model surfaces has been studied using atomistic molecular dynamics simulations. We use an ionic model to mimic mica surface charge density but without a long-range electric field above the surface, a silica model with a long-range electric field similar to that found experimentally, and an Au {111} model with no partial charges or electric field. A detailed description of the adsorption processes and the contrasts between the various model surfaces is provided. In the case of our model silica surface with a long-range electrostatic field, the adsorption is rapid and primarily driven by electrostatics. Because it is negatively charged (?1e), FN ^III9 readily adsorbs to a positively charged surface. However, due to its partial charge distribution, FN^III9 can also adsorb to the negatively charged mica model because of the absence of a long-range repulsive electric field. The protein dipole moment dictates its contrasting orientation at these surfaces, and the anchoring residues have opposite charges to the surface. Adsorption on the model Au {111} surface is possible, but less specific, and various protein regions might be involved in the interactions with the surface. Despite strongly influencing the protein mobility, adsorption at these model surfaces does not require wholesale FN^III9 conformational changes, which suggests that the biological activity of the adsorbed protein might be preserved.