Fig. 2.

Functional analysis of truncated SADS-CoV S1 proteins. (A) Protein binding activity to A549 cell surface. ΔNTD, SD1-CTD, CTD or Fc fusion proteins were incubated with adherent A549 cells at a concentration of 20 μg/mL at 4 °C. One hour later, the cells were extensively washed with PBS to remove unbound protein. Following incubation with PE anti-human IgG secondary antibody and washing, the cells were detached using 0.5 mM EDTA in PBS for FACS analysis. (B) Protein inhibition activity of SADS-CoV infection. SADS-CoV mixed with indicated concentrations of ΔNTD, SD1-CTD, CTD or Fc fusion proteins, and then added to A549 cells at a multiplicity of infection (MOI) of 0.01. Twenty-four hours later, intracellular mRNA was extracted. The relative SADS-CoV genome level was measured using quantitative RT-PCR. ****p < 0.0001, unpaired t-test.