Since CV38-142 IgG potently neutralizes infection by SARS-CoV-2 and SARS-CoV pseudoviruses (Figure1B) and in authentic virus assays (Kreye etal., 2020), this finding then poses a question about the mechanism of CV38-142 neutralization of sarbecovirus infection. enhance neutralization of SARS-CoV and SARS-CoV-2, including circulating variants of concern B.1.1.7 and B.1.351. Overall, this study provides valuable information for vaccine and therapeutic design to address Cinnamyl alcohol current and future antigenic drift in SARS-CoV-2 and to protect against zoonotic SARS-related coronaviruses. Keywords:cross-neutralizing antibody, antibody cocktail, synergy, coronavirus, SARS-CoV-2, COVID-19, antibody-antigen interaction, 3D structure, crystallography == Graphical abstract == == Highlights == X-ray and EM structures of CV38-142 with SARS-CoV-2 and SARS-CoV RBDs and spikes N343 glycan and bound waters facilitate cross-reactivity to SARS-related viruses CV38-142 synergizes with CR3022 conserved site antibodies, in particular COVA1-16 These two cross-neutralizing antibodies neutralize SARS-CoV-2 variants of concern Antibody CV38-142 from a COVID-19 patient cross-reacts with SARS-related viruses. Liu et al. reveal that CV38-142 interacts with the S309 N343 glycan site and synergizes with Cinnamyl alcohol COVA1-16 that binds the conserved CR3022 site. Combination of the two cross-neutralizing antibodies shows enhanced neutralization to circulating variants of concern B.1.1.7 and B.1.351. == Introduction == Severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2 have caused epidemics in the past two decades, including the current pandemic of coronavirus disease 2019 (COVID-19). SARS-CoV-2 has already resulted in more than 140 million reported cases and over 3 million deaths worldwide as of April 21, 2021 (https://covid19.who.int). Although these viruses have devastating consequences in the human population, they are of animal origin and have less morbidity or even no symptoms in their animal hosts (Cui et al., 2019;Tortorici and Veesler, 2019;Ye et al., 2020). In addition to these human -coronaviruses (SARS-CoV, MERS-CoV, and SARS-CoV-2), other SARS-related coronaviruses (SARSr-CoVs) of the sarbecovirus subgenus within the -coronavirus genus are found in mammalian reservoirs, such as bats and pangolins, and could also constitute potential pandemic threats to human health (Hu et al., 2015;Lam et al., 2020;Wacharapluesadee et al., 2021;Ye et al., 2020). Recently, mutations in SARS-CoV-2 were identified in farmed mink, and these viruses were found to be reciprocally transmissible between humans and farmed mink (Welkers et al., 2021), further underscoring concerns about Cinnamyl alcohol the long-term efficacy of current antibody therapies and vaccines under development (Mallapaty, 2020). Hence, identification and characterization of cross-neutralizing antibodies within the sarbecovirus subgenus are of value for design and development of therapeutics and next generation vaccines to mitigate against antigenic drift as well as future SARSr-CoV transmission to humans from the mammalian reservoir. Since the spike protein is the major surface protein on sarbecoviruses, neutralizing antibodies are targeted toward the spike, and many of these antibodies are able to prevent virus interaction with the host receptor, angiotensin-converting enzyme 2 (ACE2) (Piccoli et al., 2020;Yuan et al., 2021b). Other inhibition mechanisms also seem to be possible and are being assessed for other subsets of antibodies (Hansen et al., 2020;Piccoli et al., 2020;Pinto et al., 2020). The receptor-binding domain (RBD) of the spike protein is highly immunogenic and can induce highly specific and potent neutralizing antibodies (nAbs) against SARS-CoV-2 virus (Barnes et al., 2020a,2020b;Brouwer et al., 2020;Cao et al., 2020;Ju et al., 2020;Kreye et al., 2020;Piccoli et al., 2020;Robbiani et al., 2020;Rogers et al., 2020;Yuan et al., 2020a;Zost et al., 2020). Many of these nAbs bind to the receptor-binding motif (RBM) on the RBD (Yuan et al., 2021b). However, the breadth of these nAbs is limited as the RBM shares relatively low sequence identity among sarbecoviruses; the RBM is only 48% conserved between SARS-CoV-2 and SARS-CoV compared to 73% for the complete RBD (84% identity for non-RBM regions of the RBD). The RBD is also prone to naturally occurring mutations, along with the N-terminal domain (NTD) and other non-RBD and non-NTD regions, where insertions and deletions have also JNKK1 been found (Greaney et al., 2021b;Kemp et al., 2021;Liu et al., 2021;McCarthy et al., 2021;Starr et al., 2020;Tegally et al., 2021;Van Egeren et al., 2020;Voloch et al., 2021). Recent studies showed that many potent monoclonal nAbs are sensitive to the antigenic drift or mutation on the RBD of the spike protein (Thomson et al., 2021;Wang et al., 2021a,2021b;Weisblum et al., 2020;Wibmer et al., 2021), as well as polyclonal sera from convalescent or vaccinated individuals (Andreano et al., 2020;Greaney et al., 2021a;Liu et al., 2021;Wang et al., 2021a,2021b;Weisblum et al., 2020;Wu et al., 2021). We and others have reported cross-neutralizing antibodies such as COVA1-16, H014, EY6A, and S304 that bind to a highly conserved cryptic site in RBD of the spike (Liu et al., 2020;Lv et al., 2020;Piccoli et al., 2020;Yuan et al., 2021b;Zhou et al., 2020). Although the epitopes of these antibodies do not overlap with the ACE2 receptor-binding site, some can sterically block ACE2 binding to.