Microfluidic Diffusional Sizing applied to the study of natural products and extracts that modulate the SARS-CoV-2 SpikeRBD/ACE2 interaction - Presentation

The interaction between SARS-CoV-2 SpikeRBD and ACE2 proteins is a crucial step for host cell infection by the virus. Without it, the entire virion input mechanism is compromised. The aim of this study is to evaluate the capacity of various natural product classes to modulate this interaction. To do this, we applied a recently developed Microfluidic Diffusional Sizing (MDS) technique that allows to measure the interaction governing the protein-protein complexes via the measurement of the dissociation constant (Kd). In this method, a microfluidic chip chamber allows to monitor the diffusion of a fluorescently-labelled protein (SpikeRBD) between 2 laminar flows, giving a direct estimate of its hydrodynamic radius (Rh). The evolution of Rh is monitored in the presence of increasing concentrations of the partner protein (ACE2) and the Kd is determined through a binding curve experiment design. In a second time, with the protein partners present in equimolar amounts, the Rh of the proteins complex was measured in the presence of different natural products. Five out of the nine natural products/extracts tested have shown modulatory activity: (i) the methanol extract of Chenopodium quinoa Willd seeds husk (50 µg/mL; saponins); (ii) ivermectin (1 nM), (iii) the flavonoids naringenin (1 µM) and quercetin (150 µM); and (iv) the ethanol extract of Rhei radix (Rheum palmatum L., Rheum officinale Baillon) (100 µg/mL; anthraquinones).
This rapid selection of effective modulators will be completed by Kd measurements, by a study of their effects on cells and by crystallographic studies that will elucidate their interactions with the complex SARS-CoV-2 SpikeRBD/ACE2. This will allow to better understand agents possibly preventive against SARS-CoV-2 infection.