Figure 5. Role of amino acid residue 667 enhances SARS-CoVpp entry in the presence of airway proteases.

SARS-CoVpp (A) or R667App (B) was pre-incubated with 16HBE cells on ice for 30 min. Cells were washed twice to remove any unbound pp. Cells were incubated with 10 µg/ml of either trypsin (T), TMPRSS11a (N) or 100 µg/ml of plasmin (P) at room temperature for 40 min. Luciferase activity (LCPS) was measured from infected 16HBE cells. Asterisk (*) indicates a value of p<0.05 and (**) indicates a value of p<0.01 in two-tailed t tests. Experiments were performed in triplicates and values were expressed as means±SE from three independent experiments.