Figure 1.

Comparison of VRC and Mt. Sinai spike protein expression constructs. Both constructs contain the native spike (S) protein signal sequence (amino acids 1–14) followed by the S ectodomain (green). Furin cleavage sites (RRAR) were mutated in both constructs as noted, and stabilizing proline mutations were introduced. Both constructs contain a phage T4 fibritin trimerization domain (blue) and C-terminal purification tags (red). The Mt. Sinai construct contains a non-cleavable His6 purification tag, while the VRC construct contains a combination His8-dual Strep2 tag preceded by a rhinovirus 3C protease cleavage sequence.