Figure 5.

The SARS-CoV-2 Delta NTD or BA.2 NTD does not alter spike fusion or sensitivity to TMPRSS2 of BA.1

(A) PV bearing Delta, BA.1, BA.2, or chimeric forms of BA.1 and BA.2 spike were used to transduce Calu3, H1299, and 293T expressing endogenous levels of ACE2 and TMPRSS2 and TMPRSS2-overexpressing 293T cells.

(B) Fusion kinetics of the chimeric Delta NTD in BA.1 and BA.2 along with their parental spikes. The heatmap at each time point shows the mean of the GFP-positive area over the field of view from two experiments. The western blot showing cleavage of spike is directly underneath the heatmap.

(C) PV bearing BA.1, BA.2, or chimeras with Delta were transduced into either parental 293T cells or 293T cells overexpressing TMPRSS2. The fold increase of the virus entry in TMPRSS2-overexpressing cells over parental cells is shown above the scatterplots.

(D) The fusion assay of BA.1, BA.2, and their chimeric BA.1 bearing the BA.2 NTD and BA.2 bearing the BA.1 NTD. The line graphs show the percentage of the positive GFP area at 1 h interval post transfection. The data showing the SEM at each time point were averaged from two experiments.

(E) BA.1, BA.2, or chimeras bearing the BA.2 NTD or the BA.1 NTD together with Delta were transduced into either parental 293T cells or 293T cells overexpressing TMPRSS2. The fold increase of the virus entry in T2-overexpressing cells over parental cells is shown above the scatterplots.

In (A), (C), and (E), the plots are representative of two experiments. Mean ± SEM are shown for technical replicates (n = 4; two-sided unpaired Student’s t test). ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, ^∗∗∗∗p < 0.0001.