Protein expression and purification were conducted as described previously (Dejnirattisai et al., 2021a (link); Zhou et al., 2020 ). Briefly, plasmids encoding proteins were transiently expressed in HEK293T (ATCC CRL-11268) cells. The conditioned medium was concentrated using a QuixStand benchtop system. His-tagged Omicron RBD were purified with a 5 mL HisTrap nickel column (GE Healthcare) and further polished using a Superdex 75 HiLoad 16/60 gel filtration column (GE Healthcare). Twin-strep tagged Omicron spike was purified with Strep-Tactin XT resin (IBA lifesciences).
~4mg of ACE2 was mixed with homemade His-tagged 3C protease and DTT (final concentration 1mM). After incubated at 4 °C for one day, the sample was flown through a 5 mL HisTrap nickel column (GE Healthcare). His-tagged proteins were removed by the nickel column and purified ACE2 was harvested and concentrated.
~4mg of ACE2 was mixed with homemade His-tagged 3C protease and DTT (final concentration 1mM). After incubated at 4 °C for one day, the sample was flown through a 5 mL HisTrap nickel column (GE Healthcare). His-tagged proteins were removed by the nickel column and purified ACE2 was harvested and concentrated.
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