Fig. 2.
S1/S2 cleavage is required for MERS pp entry into Calu3 cells. (A) Vero81, Huh7, and Calu3 cells were inoculated with WT, S1/S2 mutant (YSAS and SSVR) MERS pps, or with pp-lacking S proteins (Bald). (B) Three HAE cultures were inoculated with VSV-based WT and S1/S2 mutant MERS pseuodoparticles. (C) MERS pps were pretreated with trypsin and then used to inoculate Calu3 cells. (D) MERS pps were produced in the presence of PCI, cleared free of residual PCI, and used to inoculate Calu3 cells. In all experiments, virus entry was quantified by measuring luciferase levels at 18 h (B) or at 48 h (A, C, D) posttransduction. Lower panels depict S proteins on MERS pps after Western blotting. Uncleaved (Sunc) and cleaved (S2) positions are indicated. The numbers at the left indicate molecular mass in kilodaltons. Error bars present SD from the mean (n = 3). Statistical significance was assessed by Student's t test. *P < 0.05; †P < 0.01; ‡P < 0.001; ns, not significant.