Figure 4.
Effect of residue substitution on MERS-CoV RBD binding to DPP4 (A) and entry efficiency of pseudotyped viruses (B). (A) SDS-PAGE analysis of co-purified complexes of wild-type or mutant forms of His-tagged RBD and untagged DPP4. The actual residue changes in the RBD are indicated above each lane. The DPP4 untagged serves as a negative control to exclude nonspecific binding of untagged DPP4 with Ni-NTA resin. (B) Entry efficiency of pseudotyped viruses bearing the wild-type and mutant forms of viral spike glycoprotein. The percentage of entry efficiency was calculated on the basis of luciferase activity of mutant viruses versus that of the wild-type virus. Soluble RBD (∼150 μg/ml) and DPP4 (∼150 μg/ml) were also tested for their inhibitory activity against wild-type virus. One irrelevant soluble protein with the same concentration was used as a negative control. Error bars represent SD of two replicate experiments.