Structural insights into the receptor-binding domain of bat coronavirus ZXC21.

Bat coronaviruses ZXC21 and ZC45 were discovered before the COVID-19 outbreak and share approximately 86% genome homology with SARS-CoV-2. Earlier studies indicated that ZXC21 and ZC45 may be involved in the emergence of SARS-CoV-2. However, the cell invasion mechanisms of ZXC21 and ZC45 remain unclear. Here, we determined the crystal structure of the ZXC21 receptor-binding domain (RBD) and found that the core structure shared high similarity with SARS-CoV-2, MERS-CoV, human coronavirus (HCoV)-HKU1, SARS-CoV, and HCoV-OC43 RBDs, whereas the receptor-binding motifs (RBMs) differ. We demonstrated that the ZXC21 RBD had no interaction with the human coronavirus receptors angiotensin-converting enzyme 2 (ACE2), dipeptidylpeptidase 4 (DPP4), aminopeptidase N (APN), or transmembrane serine protease 2 (TMPRSS2) by surface plasmon resonance (SPR). Moreover, the P5S-3B11 Fab can bind to the ZXC21 RBD, indicating that this SARS-CoV-2 core-targeting antibody may retain neutralizing activity toward the ZXC21 coronavirus. Our results revealed the bat coronavirus ZXC21 RBD structure, which may provide further insights into the evolution of SARS-CoV-2 and the other human beta-coronaviruses.