Anti p24 antibody

To evaluate S protein expression in the cell lysates, HEK293T cells were transfected with plasmids encoding different S proteins. At 40 h post-transfection, the cells were lysed using RIPA lysis buffer containing protease inhibitors. To determine the incorporation of S proteins into the pseudovirions, the pseudovirus-containing supernatant was pelleted through a 20% sucrose cushion at 25,000 rpm at 4 °C for 2 h. Viral pellets were resuspended in 1 × loading buffer. Cell lysates and pseudovirion pellets were separated using 10% sodium dodecyl–sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and transferred to nitrocellulose membranes. The SARS-CoV-2 S proteins were detected with a rabbit polyclonal anti-S2 antibody (Sinobiological Inc., Beijing, China), and the blot was further stained with horseradish peroxidase-conjugated goat anti-rabbit IgG and visualized with Clarity Western ECL substrate (Bio-Rad, Hercules, CA, USA). β-actin and HIV capsid protein (p24) were detected using a mouse monoclonal anti-β-actin antibody (Sigma, St. Louis, MO, USA) and a rabbit polyclonal anti-p24 antibody (Sinobiological Inc., Beijing, China), respectively.

Protein samples extracted from cells were conducted SDS polyacrylamide gel electrophoresis and transferred onto Nitrocellulose membrane. Proteins on NC membrane were immunoblotted with anti-VSV G antibody (1:12,000; Santa Cruz, sc-66180), anti-p24 antibody (1:30,000; Sino Biological Inc.), or anti-β-actin antibody (1:10,000; Sigma-Aldrich, A5441) and then with secondary antibodies. Antibodies bound protein bands were detected by ECL plus western blot system (PerkinElmer, Waltham, MA, USA).