Adsorption Orientation and Binding Motifs of Lysozyme and Chymotrypsin on Amorphous Silica

Abstract

The adsorption of α-chymotrypsin and hen egg white lysozyme on amorphous silica is studied by molecular dynamics (MD) simulations in comparison with adsorption experiments. Protein–surface interaction profiles are computed in implicit solvent at the level of DLVO theory. These reveal a preferential adsorption orientation for chymotrypsin, driven by its large dipole moment, with its α-helical regions pointing toward the surface. Instead, a less clear orientational preference characterizes lysozyme adsorption, which approaches the surface in a side-on orientation, confirming previous results. Explicit-solvent MD simulations are then performed to analyze the formation and stability of protein–surface contacts. While no significant conformational changes take place in the short simulation time investigated (up to 300 ns), the simulations clearly reveal the presence of adsorption motifs comprising both positively charged, but also negatively charged, polar and even nonpolar residues. Stable adsorption originates from a favorable match between the adsorption motifs and the local subnanometer distribution of charged, strongly hydrophilic, and less hydrophilic surface regions. We conclude that intuitive arguments based on DLVO forces may be put forward to predict the expected adsorption orientation of the proteins. However, observed differences in the relative adsorption amount of the two enzymes can only be explained by taking into account also protein–protein interactions and the stability of the aforementioned specific adsorption motifs.

Electrostatically Driven Protein Adsorption: Charge Patches versus Charge Regulation

“…It is worthwhile to compare the results in Figure 4 with the predictions of constant-charge MD simulations in literature, which modelled the adsorption of lysozyme on negatively charged silica surfaces at pH 7 49,50 and 8. 51 The orientation predicted by our model for lysozyme at its isoelectric point (pH 11.2) on a negative surface is very close to the most stable orientation predicted by these MD simulations. [49][50][51][52] Moreover, MD studies have identified the same aminoacids as our study (Lys1, Arg5, Arg125 and Arg128) as the aminoacids that reside closest to the surface and contribute the most to the interaction with the silica substrate.…”

Steering protein adsorption at charged surfaces: electric fields and ionic screening

“…Key questions that still need to be addressed concern not only the extent of protein adsorption, i.e. whether complete surface coverage or even multilayer coverage is achieved, but also the strength of the adhesion to the surface and the functionality of the adsorbed protein [9][10][11][12][13][14] . These factors directly the affect the utility of the adsorbed proteins for functionalization of surfaces to induce biocompatibility, create antibacterial coatings, or yield novel nanoparticulate drug delivery systems 1 .…”

Stable Molecular Diodes Based on π–π Interactions of the Molecular Frontier Orbitals with Graphene Electrodes

“…We found a near‐symmetrical energy barrier of ≈0.3 eV for rotation of the molecule on graphene between edge‐on and end‐on Fc binding modes. This rotational barrier is almost identical to that computed for model proteins interacting with silica substrates, and is half of that calculated between hydrocarbon dimers . Fokin et al also verified that the Perdew–Burke–Ernzerhof (PBE) functionals outperform the majority of hybrid functionals as regards matching experimental energy barrier data.…”