days, the supernatant was collected and loaded to Ni-NTA resin for purification. The elution was concentrated and further purified by a Superdex 200 column.

In-Gel Analysis of SARS-CoV-2 S and Human ACE2 Proteins
A 3.5-μg aliquot of SARS-CoV-2 S protein as well as a 2-μg aliquot of human ACE2 were combined