DPP4 and infection: MERS-CoV Spike glycoprotein is composed of an N-terminal S1 subunit, which is assembled as four domains (A–D) and controls attachment to dipeptidyl-peptidase 4 (DPP4, the host receptor), and a C-terminal S2 subunit that combines the viral and cellular membranes to initiate infection, as shown in Figure 5 [111].