Spike protein receptor-binding domains from SARS-CoV-2 variants of interest bind human ACE2 more tightly than the prototype spike protein

Several SARS-CoV-2 variants of interest (VOI) have emerged since this virus was first identified as the etiologic agent responsible for COVID-19. Some of these variants have demonstrated differences in both virulence and transmissibility, as well as in evasion of immune responses in hosts vaccinated against the original strain of SARS-CoV-2. There remains a lack of definitive evidence that identifies the genetic elements that are responsible for the differences in transmissibility among these variants. One factor affecting transmissibility is the initial binding of the surface spike protein (SP) of SARS-CoV-2 to human angiotensin converting enzyme-2 (hACE2), the widely accepted receptor for SP. This step in the viral replication process is mediated by the receptor binding domain (RBD) of SP that is located on the surface of the virus. This current study was conducted with the aim of assessing potential differences in binding affinity between recombinant hACE2 and the RBDs of emergent SARS-CoV-2 WHO VOIs. Mutations that affect the binding affinity of SP play a dominant initial role in the infectivity of the virus.