A high-affinity RBD-targeting nanobody improves fusion partner’s potency against SARS-CoV-2

A key step to the SARS-CoV-2 infection is attachment of its Spike receptor-binding domain (S RBD) host receptor ACE2. Considerable research has been devoted development neutralizing antibodies, including llama-derived single-chain nanobodies, target motif (RBM) and block ACE2-RBD binding. Simple effective strategies increase potency are desirable for such studies when antibodies only modestly effective. Here, we identify characterize a high-affinity synthetic nanobody (sybody, SR31) as fusion partner improve RBM-antibodies. Crystallographic reveal that SR31 binds RBD at conserved ‘greasy’ site distal RBM. Although distorts interface, it does not perturb RBM conformation, hence displaying no activities itself. However, fusing two sybodies dramatically increases their affinity neutralization activity against pseudovirus. Our work presents tool protein an efficient strategy potency.