SARS-CoV-2, the virus causing COVID-19, uses its spike (S) protein to infect host cells. The S protein is cleaved by the host protease furin into two parts, S1 and S2. The S1 fragment contains a polybasic sequence (RRAR) that conforms to the C-end rule (CendR) motif, which binds to cell surface receptors neuropilin-1 (NRP1) and NRP2. This interaction is critical for SARS-CoV-2 entry and infection. Using x-ray crystallography and biochemical methods, the study shows that the S1 CendR motif directly binds to NRP1. Blocking this interaction reduced SARS-CoV-2 entry and infectivity in cell culture. NRP1 thus serves as a host factor for SARS-CoV-2 infection and may be a therapeutic target for COVID-19. The CendR motif in S1 is recognized by NRP1, which is involved in various biological processes. Experiments showed that NRP1 interacts with S1 and enhances SARS-CoV-2 infection. In cell lines expressing ACE2, NRP1 knockout reduced SARS-CoV-2 infection, indicating NRP1's role in viral entry. The study also found that NRP1 binding to the S1 CendR motif is essential for viral entry, as mutations in NRP1 or the S1 CendR motif reduced this interaction. The study further demonstrated that the interaction between S1 and NRP1 can be inhibited by small molecule antagonists, such as EG00229, which binds to the NRP1 b1 domain and reduces SARS-CoV-2 infection. These findings suggest that targeting the S1-NRP1 interaction could be a potential therapeutic strategy for COVID-19. The study highlights the importance of NRP1 in SARS-CoV-2 infection and provides a molecular basis for the interaction between the virus and its host cell receptors. The results suggest that NRP1 may play a role in the increased infectivity of SARS-CoV-2 compared to SARS-CoV. Targeting this interaction could offer a new approach for treating COVID-19.SARS-CoV-2, the virus causing COVID-19, uses its spike (S) protein to infect host cells. The S protein is cleaved by the host protease furin into two parts, S1 and S2. The S1 fragment contains a polybasic sequence (RRAR) that conforms to the C-end rule (CendR) motif, which binds to cell surface receptors neuropilin-1 (NRP1) and NRP2. This interaction is critical for SARS-CoV-2 entry and infection. Using x-ray crystallography and biochemical methods, the study shows that the S1 CendR motif directly binds to NRP1. Blocking this interaction reduced SARS-CoV-2 entry and infectivity in cell culture. NRP1 thus serves as a host factor for SARS-CoV-2 infection and may be a therapeutic target for COVID-19. The CendR motif in S1 is recognized by NRP1, which is involved in various biological processes. Experiments showed that NRP1 interacts with S1 and enhances SARS-CoV-2 infection. In cell lines expressing ACE2, NRP1 knockout reduced SARS-CoV-2 infection, indicating NRP1's role in viral entry. The study also found that NRP1 binding to the S1 CendR motif is essential for viral entry, as mutations in NRP1 or the S1 CendR motif reduced this interaction. The study further demonstrated that the interaction between S1 and NRP1 can be inhibited by small molecule antagonists, such as EG00229, which binds to the NRP1 b1 domain and reduces SARS-CoV-2 infection. These findings suggest that targeting the S1-NRP1 interaction could be a potential therapeutic strategy for COVID-19. The study highlights the importance of NRP1 in SARS-CoV-2 infection and provides a molecular basis for the interaction between the virus and its host cell receptors. The results suggest that NRP1 may play a role in the increased infectivity of SARS-CoV-2 compared to SARS-CoV. Targeting this interaction could offer a new approach for treating COVID-19.