Size exclusion chromatography
The oligomerization state of the recombinant S protein was evaluated by
high-resolution size exclusion chromatography (SEC). Elution fractions
from IMAC containing purified S protein were collected and concentrated,
and the buffer was exchanged and loaded on a Superdex 200 increase
10/300 (Cytiva, Marlborough, USA) equilibrated in 100 mM sodium
phosphate buffer, 150 mM NaCl, pH 7.4. All fractions were collected, and
the S protein was revealed by WB using an anti-6x His-tag antibody, as
described previously. The calculated molecular weight (MW) of the
expressed protein, without considering the glycan moieties, was 138914
Da.