Comment by subroutine

Comparing the protein sequence between the virus and vaccine, it looks like codons 986 and 987 code for different amino acids. I looked it up and it seems like a very important bioengineered constraint. Membrane fusion can be blocked by mutating S residues 986 and 987 to prolines, producing an S antigen stabilised in the prefusion conformation. The introduction of this two-proline substitution yields soluble prefusion coronavirus S ectodomains (overcoming a major hurdle in subunit vaccine dev).