As the binding of the S protein receptor-binding domain (RBD) to the human host receptor angiotensin-converting enzyme 2 (ACE2) is considered the most important step in viral infection, any changes in this region, particularly within the receptor-binding motif (RBM), may result in improved or weakened virus binding to the host (Lan et al., 2020). Here, ACE2 is linked to viral infectious disease.