The N121T and N121S substitutions on the spike protein of SARS-CoV-2 have a greater impact on serum neutralization reactions compared to biliverdin binding

The N121 site on the spike N-terminal domain (NTD) of SARS-CoV-2 is known to be associated with heme and its metabolite, biliverdin, which can affect antibody binding. Either N121T or N121S substitutions have been observed in natural conditions as well as in a hamster model of dual infection with SARS-CoV-2 and Influenza A virus. Through serum neutralization tests using lentivirus-based pseudoviruses expressing WT, N121T, and N121S spikes with both mouse and human sera, it was observed that the N121T and N121S mutations had a greater impact on neutralizing antibody reactions compared to biliverdin treatment. Although N121T and N121S substitutions are not currently major variants in recent SARS-CoV-2 strains, this study could provide fundamental information to prepare for potential future mutations at the N121 site of SARS-CoV-2.