Structure of the SARS-CoV-2 spike receptor-binding domain bound to the ACE2 receptor

A new and highly pathogenic coronavirus (severe acute respiratory syndrome coronavirus-2,SARS-CoV-2) caused an outbreak in Wuhan city,Hubei province,China,starting from December 2019 that quickly spread nationwide and to other countries around the world1 ,2 ,3. Here,to better understand the initial step of infection at an atomic level,we determined the crystal structure of the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 bound to the cell receptor ACE2. The overall ACE2-binding mode of the SARS-CoV-2 RBD is nearly identical to that of the SARS-CoV RBD,which also uses ACE2 as the cell receptor4. Structural analysis identified residues in the SARS-CoV-2 RBD that are essential for ACE2 binding,the majority of which either are highly conserved or share similar side chain properties with those in the SARS-CoV RBD. Such similarity in structure and sequence strongly indicate convergent evolution between the SARS-CoV-2 and SARS-CoV RBDs for improved binding to ACE2,although SARS-CoV-2 does not cluster within SARS and SARS-related coronaviruses1 ,2 ,3 ,5. The epitopes of two SARS-CoV antibodies that target the RBD are also analysed for binding to the SARS-CoV-2 RBD,providing insights into the future identification of cross-reactive antibodies.

ACE-2-like Enzymatic Activity in Anti-SARS-CoV-2 Spike Protein Monoclonal Antibodies

Many people are affected by post-acute sequelae of COVID-19 (PASC/long COVID, LC). LC has severely affected public health. Features of LC including blood pressure dysregulation, coagulopathies, hyperinflammation, and neuropsychiatric complaints. Mechanisms responsible for LC pathogenesis are not clear. The receptor for SARS-CoV-2 is human angiotensin converting enzyme 2 (ACE2), which binds SARS-CoV-2 spike protein receptor-binding domain (RBD) to initiate infection. We hypothesized that some people produce anti-RBD antibodies that sufficiently resemble ACE2 structure to have ACE2-like catalytic activity. Those antibodies, ACE2-like abzymes, may contribute to LC pathogenesis. We previously showed that ACE2-like activity was associated with immunoglobulin in some people with acute and convalescent COVID-19. ACE2-like catalytic activity correlated with blood pressure changes following moderate exercise challenge in convalescents. We screened human monoclonal antibodies (mAbs) against SARS-CoV-2 spike protein from 4 sources. We identified 4 human mAbs with ACE2-like catalytic activity. The activity was not inhibited by MLN-4760, a compound that inhibits native human ACE2, nor by EDTA, unlike native ACE2, a Zinc metalloprotease, but was inhibited by an overlapping pool of Spike peptides. Enzyme kinetic studies showed that the mAbs had lower Vmax and Km values than ACE2. The data suggested that the antibodies cleave angiotensin II via a different mechanism than ACE2. Identification of mAbs with ACE2-like catalytic activity supports the hypothesis that antibodies induced by SARS-CoV-2 infection could help mediate the pathogenesis of COVID-19 and LC, and more generally, the hypothesis that catalytic antibodies induced by infectious agents can contribute to disease pathogenesis.