Mechanistic Insights into Protein Corona Formation: The Surface Charge of Mesoporous Silica Nanoparticles Determines the Orientation and the Conformation of Adsorbed BSA Protein

The formation of the protein corona critically governs the biological identity of nanoparticles, but the molecular determinants of protein orientation and conformational fate remain elusive. Here, we examine the adsorption of bovine serum albumin (BSA), a prototypical dysopsonin, onto bare and amino-functionalized mesoporous silica nanoparticles (MSN and MSN-NH₂) at physiological pH. Zeta potential titrations, quartz crystal microbalance with dissipation monitoring (QCM-D), and circular dichroism (CD) spectroscopy reveal robust binding of BSA to both negatively charged MSN and positively charged MSN-NH₂. QCM-D quantification indicates enhanced adsorption on MSN-NH₂ (481 ng cm^-2) relative to that on MSN (228 ng cm^-2), consistent with attractive electrostatic interactions. Strikingly, substantial BSA adsorption also occurs on MSN, even though both species carry negative zeta potentials. This indicates orientation-dependent interactions driven by the heterogeneous charge distribution of BSA, likely involving domain III binding to the silica surface. CD spectroscopy further demonstrates that the nanoparticle surface charge dictates the BSA secondary structure: the α-helix content decreases from 60% to 25%, while β-sheet and random coil fractions increase upon adsorption to MSN-NH₂. Whereas BSA retains its native (N) conformation on MSN, it undergoes pronounced distortion toward fast (F) or elongated (E) states on MSN-NH₂. These findings establish that nanoparticle surface charge governs not only the adsorption extent but also protein orientation and conformational fate, thereby shaping protein corona formation and its downstream biological identity.