Spin Label Study of the Orientational Preferences of Lysozyme in a Bioinspired Silica Composite

Polycationic polypeptides prompt the polycondensation of inorganic oxides, most notably of silica. Hen egg-white lysozyme is a small polycationic protein that is quite conveniently used to this end. The fate of the protein after the completion of the polycondensation reaction is still a matter of debate. We have recently proven that lysozyme strongly interacts with silica. In this study, we use spin-label-based EPR spectroscopy to investigate whether the protein shows an orientational preference with respect to the silica surface within the composite. We find that a large share of the protein behaves as when it is adsorbed on pre-formed silica, albeit with a more marked preference for orientations that point the patches with higher surface charge density toward the material. In addition, a part of the protein shows a less-defined behavior. With this study, we provide additional information on the nature of the protein-material interactions in this class of bioinspired solids.