The RBM of MERS-CoV S1-CTD mainly consists of a four-stranded β-sheet, in contrast to the loop-dominated RBM in  SARS-CoV S1-CTD . Like the VBM for SARS-CoV on ACE2, the VBM for MERS-CoV is also located on the outer surface of DPP4, away from the peptidase active site.Whereas the conserved core structures of SARS-CoV and MERS-CoV S1-CTDs indicate a divergent evolutionary pathway that has led to their recognition of different host receptors. THe S1-CTDs of MERS-CoV and a highly related bat coronavirus HKU4 recognize DPP4 in very similar ways, suggesting a close evolutionary relationship between the two viruses.