The study investigates the interaction between the SARS-CoV-2 spike (S) protein and neuropilin-1 (NRPI), a host receptor involved in viral entry. The S protein, upon cleavage by the host protease furin, generates a polybasic Arg-Arg-Ala-Arg (RRAR) sequence at the S1/S2 boundary, which binds to NRPI through a C-end rule (CendR) motif. Using x-ray crystallography and biochemical methods, the researchers confirmed that the S1 CendR motif directly binds to NRPI. Blocking this interaction through RNA interference or selective inhibitors reduced SARS-CoV-2 entry and infectivity in cell culture. The study also found that NRPI knockout cells showed significantly reduced SARS-CoV-2 infection compared to wild-type cells. Additionally, the researchers identified monoclonal antibodies and a small molecule antagonist that target the NRPI b1 domain and inhibit the interaction, thereby reducing viral infectivity. These findings suggest that NRPI serves as a host factor for SARS-CoV-2 infection and could be a potential therapeutic target for COVID-19.The study investigates the interaction between the SARS-CoV-2 spike (S) protein and neuropilin-1 (NRPI), a host receptor involved in viral entry. The S protein, upon cleavage by the host protease furin, generates a polybasic Arg-Arg-Ala-Arg (RRAR) sequence at the S1/S2 boundary, which binds to NRPI through a C-end rule (CendR) motif. Using x-ray crystallography and biochemical methods, the researchers confirmed that the S1 CendR motif directly binds to NRPI. Blocking this interaction through RNA interference or selective inhibitors reduced SARS-CoV-2 entry and infectivity in cell culture. The study also found that NRPI knockout cells showed significantly reduced SARS-CoV-2 infection compared to wild-type cells. Additionally, the researchers identified monoclonal antibodies and a small molecule antagonist that target the NRPI b1 domain and inhibit the interaction, thereby reducing viral infectivity. These findings suggest that NRPI serves as a host factor for SARS-CoV-2 infection and could be a potential therapeutic target for COVID-19.