Pathogen-Host Adhesion between SARS-CoV-2 S Proteins from Different Variants and Human ACE2 Probed at Single-Molecule and Single-Cell Levels

Pathogen-Host adhesion is considered the first step of infection for many pathogens such as bacteria and virus. The binding of the receptor binding domain (RBD) of SARS-CoV-2 Spike protein (S protein) onto human angiotensin-converting enzyme 2 (ACE2) is considered as the first step for the SARS-CoV-2 to adhere onto the host cells during the infection. Within three years, a number of variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been found all around the world. Here, we investigated the adhesion of S Proteins from different variants and ACE2 using atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) and single-cell force spectroscopy (SCFS). We found that the unbinding force and binding probability of the S protein from Delta variant to the ACE2 was the highest among the variants tested in our study at both single-molecule and single-cell levels. Molecular dynamics simulation showed that ACE2-RBD (Omicron) complex is destabilized by the E484A and Y505H mutations and stabilized by S477N and N501Y mutations, when compared with Delta variant. In addition, a neutralizing antibody, produced by immunization with wild type RBD of S protein, could effectively inhibit the binding of S proteins from wild type, Delta and Omicron variants onto ACE2. Our results provide new insight for the molecular mechanism of the adhesive interactions between S protein and ACE2 and suggest effective monoclonal antibody can be prepared using wild type S protein against the Delta and Omicron variants by inhibit the pathogen-host adhesion. ### Competing Interest Statement The authors have declared no competing interest.