The spillovers of β-coronaviruses in humans and the emergence of SARS-CoV-2 variants highlight the need for broad coronavirus countermeasures. We describe five monoclonal antibodies (mAbs) cross-reacting with the stem helix of multiple β-coronavirus spike glycoproteins isolated from COVID-19 convalescent individuals. Using structural and functional studies we show that the mAb with the greatest breadth (S2P6) neutralizes pseudotyped viruses from three different subgenera through inhibition of membrane fusion and delineate the molecular basis for its cross-reactivity. S2P6 reduces viral burden in hamsters challenged with SARS-CoV-2 through viral neutralization and Fc-mediated effector functions. Stem helix antibodies are rare, oftentimes of narrow specificity and can acquire neutralization breadth through somatic mutations. These data provide a framework for structure-guided design of pan-β-coronavirus vaccines eliciting broad protection.

Ligand–receptor interactions that are reinforced by mechanical stress, so-called catch-bonds, play a major role in cell–cell adhesion. They critically contribute to widespread urinary tract infections by pathogenic Escherichia coli strains. These pathogens attach to host epithelia via the adhesin FimH, a two-domain protein at the tip of type I pili recognizing terminal mannoses on epithelial glycoproteins. Here we establish peptide-complemented FimH as a model system for fimbrial FimH function. We reveal a three-state mechanism of FimH catch-bond formation based on crystal structures of all states, kinetic analysis of ligand interaction and molecular dynamics simulations. In the absence of tensile force, the FimH pilin domain allosterically accelerates spontaneous ligand dissociation from the FimH lectin domain by 100,000-fold, resulting in weak affinity. Separation of the FimH domains under stress abolishes allosteric interplay and increases the affinity of the lectin domain. Cell tracking demonstrates that rapid ligand dissociation from FimH supports motility of piliated E. coli on mannosylated surfaces in the absence of shear force.

our coronaviruses mainly associated with common cold-like symptoms are endemic in humans, namely OC43, HKU1, NL63 and 229E, while three highly pathogenic zoonotic coronaviruses have emerged in the past two decades, leading to epidemics and a pandemic. Severe acute respiratory syndrome coronavirus (SARS-CoV) was discovered in Guangdong Province in China in 2002 and spread to five continents through air travel routes, infecting 8,098 people and causing 774 deaths. No cases were reported after 2004 1,2 . In 2012, Middle East respiratory syndrome coronavirus (MERS-CoV) emerged in the Arabian Peninsula, where it still circulates. It was exported to 27 countries, infecting a total of 2,494 individuals and claiming 858 lives as of January 2020 according to the World Health Organization 3 . A recent study further suggested that undetected zoonotic MERS-CoV transmissions are currently occurring in Africa 4 . A novel coronavirus, named SARS-CoV-2, was associated with an outbreak of severe pneumonia in Hubei Province, China, at the end of 2019 and has since infected over 121 million people and claimed more than 2.6 million lives worldwide during the ongoing COVID-19 pandemic 5,6 .SARS-CoV and SARS-CoV-2 probably originated in bats 5,7-10 , with masked palm civets and racoon dogs acting as intermediate amplifying and transmitting hosts for SARS-CoV [11][12][13] . Although MERS-CoV was also suggested to have originated in bats, repeated zoonotic transmissions occurred from dromedary camels 14,15 . The identification of numerous coronaviruses in bats, including viruses related to SARS-CoV-2, SARS-CoV and MERS-CoV, along with evidence of spillovers of SARS-CoV-like viruses to humans, strongly indicates that future coronavirus emergence events will continue to occur 5,[7][8][9][10][16][17][18][19][20] .The coronavirus spike (S) glycoprotein mediates entry into host cells and comprises two functional subunits mediating attachment to host receptors (S 1 subunit) and membrane fusion (S 2 subunit) [21][22][23][24][25][26][27] . As the S homotrimer is prominently exposed at the viral surface and is the main target of neutralizing antibodies (Abs), it is a focus of therapeutic and vaccine design efforts 28 . We previously showed that the SARS-CoV-2 receptor-binding domain (RBD, part of the S 1 subunit) is immunodominant, comprises multiple distinct antigenic sites, and is the target of 90% of the neutralizing activity present in COVID-19 convalescent plasma 29 . Accordingly, monoclonal Abs (mAbs) with potent neutralizing activity have been identified against the SARS-CoV-2, SARS-CoV and MERS-CoV RBDs and shown to protect against viral challenge in vivo [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] . The isolation of S309 from an individual recovered from SARS-CoV, which neutralizes SARS-CoV-2 and SARS-CoV through recognition of a conserved RBD epitope, demonstrated that potent neutralizing mAbs could inhibit β-coronaviruses belonging to different lineage B (sarbecovirus) clades 31 . An optimized version of S...

Three highly pathogenic β-coronaviruses crossed the animal-to-human species barrier in the past two decades: SARS-CoV, MERS-CoV and SARS-CoV-2. SARS-CoV-2 has infected more than 64 million people worldwide, claimed over 1.4 million lives and is responsible for the ongoing COVID-19 pandemic. We isolated a monoclonal antibody, termed B6, cross-reacting with eight β-coronavirus spike glycoproteins, including all five human-infecting β-coronaviruses, and broadly inhibiting entry of pseudotyped viruses from two coronavirus lineages. Cryo-electron microscopy and X-ray crystallography characterization reveal that B6 binds to a conserved cryptic epitope located in the fusion machinery and indicate that antibody binding sterically interferes with spike conformational changes leading to membrane fusion. Our data provide a structural framework explaining B6 cross-reactivity with β-coronaviruses from three lineages along with proof-of-concept for antibody-mediated broad coronavirus neutralization elicited through vaccination. This study unveils an unexpected target for next-generation structure-guided design of a pan-coronavirus vaccine.