Fig. 6.

Identification of the S glycoprotein receptor-binding domain (RBD). (A) Comparison of the binding of two different S soluble fragments (S537 and S756) to 293 and Vero E6 cells. (B) Binding of various S fragments to Vero E6 cells. The background OD405 measured for the negative control was subtracted from the OD405s of each S fragment. The resulting OD405 for each fragment was then presented as a percentage of the OD405 for S537. (C) Interaction of S fragments with purified soluble ACE2 as measured by ELISA. In all experiments, the negative control (NC) represents sample processed exactly the same way as the others except that the plasmid used for transfection did not encode any protein. Data shown here represent at least three independent experiments. OD405 for all samples is presented as percentages of that for S537.