SARS-CoV-2 enters human cells by engaging the ACE2 receptor through the receptor-binding domain (RBD) in its spike protein. This RBD, located within the S1 subunit, is responsible for the initial viral attachment and is a major target for neutralizing antibodies and vaccine strategies. Blocking this interaction is a key approach in antiviral drug development.

Reference: https://link.springer.com/chapter/10.1007/978-3-031-46545-1_13

"Antigen Grade" is not a formally regulated industry standard, but it is commonly used to indicate that a protein is intended for antigen-based applications rather than functional assays.

Antigen Grade proteins are recombinant proteins purified under denaturing conditions (e.g., in urea) and may not retain their native conformation or biological activity. These proteins are suitable for antigen-based applications such as antibody generation, ELISA plate coating, Western blotting, and other immunological assays, but are not recommended for functional or activity assays.

Suitable Applications:

Not Recommended:

Why "Antigen Grade"?

Many bacterial proteins expressed as inclusion bodies are purified in 6–8 M urea. Although they can often be refolded, proteins sold in urea are generally not guaranteed to be correctly refolded or biologically active. "Antigen Grade" proteins are suitable for immunological applications but may not be appropriate for assays requiring native protein function.