The SARS-CoV-2 S2 protein (Spike glycoprotein subunit 2) is localized at the C-terminus of the Spike protein and mediates membrane penetration and virus–cell fusion through the presence of so called heptad repeats. The SARS-CoV-2 Spike-S2 (insect cells) protein covers amino acids S686 to K1211 and contains the stabilizing proline substitutions at position K986P and V987P. The protein is extended at its C-terminus with a His-tag and an AviTag
TM
.