Immunological challenges of the “new” infections: corona viruses

Mimicking Pseudo-Virion Interactions with Abiotic Surfaces: Deposition of Polymer Nanoparticles with Albumin Corona

Adsorption of human serum albumin (HSA) molecules on negatively charged polystyrene microparticles was studied using the dynamic light scattering, the electrophoretic and the solution depletion methods involving atomic force microscopy. Initially, the physicochemical characteristics of the albumin comprising the hydrodynamic diameter, the zeta potential and the isoelectric point were determined as a function of pH. Analogous characteristics of the polymer particles were acquired, including their size and zeta potential. The formation of albumin corona on the particles was investigated in situ by electrophoretic mobility measurements. The size, stability and electrokinetic properties of the particles with the corona were also determined. The particle diameter was equal to 125 nm, which coincides with the size of the SARS-CoV-2 virion. The isoelectric point of the particles appeared at a pH of 5. The deposition kinetics of the particles was determined by atomic force microscopy (AFM) under diffusion and by quartz microbalance (QCM) under flow conditions. It was shown that the deposition rate at a gold sensor abruptly vanished with pH following the decrease in the zeta potential of the particles. It is postulated that the acquired results can be used as useful reference systems mimicking virus adsorption on abiotic surfaces.

SARS-CoV-2 Spike Protein (RBD) Subunit Adsorption at Abiotic Surfaces and Corona Formation at Polymer Particles

The adsorption kinetics of the SARS-CoV-2 spike protein subunit with the receptor binding domain at abiotic surfaces was investigated. A combination of sensitive methods was used such as atomic force microscopy yielding a molecular resolution, a quartz microbalance, and optical waveguide lightmode spectroscopy. The two latter methods yielded in situ information about the protein adsorption kinetics under flow conditions. It was established that at pH 3.5-4 the protein adsorbed on mica and silica surfaces in the form of compact quasi-spherical aggregates with an average size of 14 nm. The maximum coverage of the layers was equal to 3 and 1 mg m^-2 at pH 4 and 7.4, respectively. The experimental data were successfully interpreted in terms of theoretical results derived from modeling. The experiments performed for flat substrates were complemented by investigations of the protein corona formation at polymer particles carried out using in situ laser Doppler velocimetry technique. In this way, the zeta potential of the protein layers was acquired as a function of the coverage. Applying the electrokinetic model, these primary data were converted to the dependence of the subunit zeta potential on pH. It was shown that a complete acid-base characteristic of the layer can be acquired only using nanomolar quantities of the protein.