Receptor-binding motif (RBM) of 2019 Coronavirus SARS-CoV-2 surface glycoprotein. This receptor-binding domain (RBD) a critical determinant of virus-receptor interaction and thus of viral host range and tropism. The RBD also includes important viral-neutralizing epitopes (21–23), and it may be sufficient to raise a protective antibody response in inoculated animals.
A total of nine cysteine residues are found in the RBD, six of which forming three pairs of disulfide bonds. Among these three pairs, two are in the core (Cys336-Cys361 and Cys379-Cys432) to help stabilize the beta sheet structure while the remaining one (Cys480-Cys488) connects loops in the distal end of the RBM.
Studies showed that the sequence of 2019-nCoV coronavirus RBD, including its receptor -binding motif (RBM) that directly contacts ACE2 and uses ACE2 as its receptor with much higher affinity (10-20 times higher!) than SARS.