Subtle structural changes in viral RBDs can lead to a complete receptor switch. For example, HCoV-NL63 and PRCV recognize two different protein receptors using structurally conserved S1-CTDs with divergent RBMs, and so do SARS-CoV and MERS-CoV. Moreover, MHV and BCoV S1-NTDs recognize a protein receptor and a sugar receptor, respectively, through subtle conformational changes in receptor-binding loops.