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. 2022 Apr 29;39(7):110829. doi: 10.1016/j.celrep.2022.110829

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The Delta spike P681R mutation improves spike protein processing

(A) Spike cleavages of purified virions. USA/WA1-2020, Alpha, Delta, and Delta-P681 viruses were purified and analyzed by western blot using polyclonal antibodies against spike and anti-nucleocapsid antibodies. Full-length (FL) spike, cleaved S1/S2, and S2′ proteins were annotated.

(B) Intracellular spike cleavages. C-terminally HA-tagged USA/WA1-2020 wild-type, P681H, and P681R mutant spikes were expressed in 293T cells. Total cell lysates were analyzed by western blot using anti-HA antibody. For both (A) and (B), one representative image of three independent experiments is shown. The densitometry was quantified by ImageLab 6.0.1 (BioRad). The ratios of S1/S2 or S2 subunits over FL spike are indicated at the top of the western blots.