One of the first steps in understanding a virus’ mode of action is to understand how it infects host cells. Apart from its RNA or DNA, a virus will have a more or less complex envelope that on one hand acts as a carrier for the nucleic acids and on the other hand enables binding and then entering a host cell. Proteins present on the outside surface of host cells are ideal targets for viral proteins to attach themselves to. In the case of the SARS-CoV-2 virus, cells that present angiotensin converting enzyme 2 receptor (ACE2) can be targeted by the virus, because the virus has spike proteins on its outer membrane with a receptor binding domain (RBD) that can bind the ACE2 receptor on the cell.

Understanding how the virus binds a host cell gives clues on development of therapeutics that are able to block this binding. Also, the presence and location of host cell proteins in the human body lends clues as to how a virus enters and spreads in the body. In the case of coronavirus, ACE2 is found –though not exclusively- in the nose, mouth, lungs and small intestine which means that these organs are likely points of entry for the virus.
Multiplex SPR can be used to investigate an array with viral proteins suspected to be involved with host cell binding by injecting potential host cell receptors over the array with viral proteins.

Figure above:The receptor binding domain (RBD) of the S1 Spike protein present on the outside of the coronavirus can bind to ACE2 receptor on the outside of human host cells. This in turn facilitates the infection of the host cell.