Fig. 1.

Expression and purification of truncated SADS-CoV S1 fusion proteins. (A) The structure of the SADS-CoV S1 (PDB code: 6 M39) monomer was displayed by PyMOL software (left). The NTD, CTD, SD1 and SD2 domains of S1 are labeled cyan, green, magenta and yellow, respectively. NTD, N-terminal domain; CTD, C-terminal domain; and SD1 to SD2, subdomains 1 to 2. The DNA sequences of CTD with distinct subdomains fused with Fc and a strep tag (right) were cloned into a pcDNA3.1 eukaryotic protein expression vector. The DNA sequence of the IFNA1 signal peptide was added between the Kozaka sequence and the CTD sequence to promote protein secretion. (B) Truncated S1 fusion proteins were expressed on Freestyle 293F cells. Proteins purified from supernatants were analyzed by Western blotting (left), silver staining (middle) and Coomassie blue staining (right) respectively. Fc-strep fusion protein was used as the negative control.