Yes a personal favorite of papers! It confirmed with structure many of our conclusions (without structure), less about the exact location of the fusion peptide, but more about the sequence of appearance of the fusion intermediate steps!

lol but honestly Ryan thanks for all your work, stringing different findings together to reveal holistic insights! 🫡🫡🫡

We thank #everyone (lol) involved, for we could not have done it without these efforts, and this includes you as well, anonymous reviewers!

What about stem-helix antibody mechanism? Because H655Y-stabilized S “extended intermediate” also prolonged the effective time window of stem-helix antibodies, their binding epitopes must only be fully exposed in this S conformation, and required for effective neutralization! 9/9

How could a SLOWER entry benefit SARS-CoV-2? The key may be on the ciliated nasal epithelial cells, where slowing could enable more viral entry on not the cilia but the cell body for more productive infections. The same delay can show up in cell cultures as “endosomal entry”. 8/9

In conclusion, S cap must still be present for S “extended intermediate” formation, where H655Y affects its durability. While H655Y delays #SARSCoV2 entry kinetics at a late stage, Omicron BA.1 compensates likely by acquiring a higher binding affinity for receptor hACE2. 7/9

Mechanistically, H655Y stabilized the “extended intermediate” S, prolonging the time HR2 peptides can bind to its transiently exposed S epitope, actually delaying the total time needed for entry. Interestingly, tighter hACE2-binding BA.1 S1B (RBD) compensated for this delay. 6/9

because H655 is part of the S cap believed to be shed early on, hence should not affect S functions past S2’ activation. Contrary to this belief, H655Y sensitized S for HR2 peptides, a conformation-specific inhibitor for the downstream “extended intermediate” S structure. 5/9

H655 is more than 5 nm away from the stem-helix antibody binding site, making it unlikely to be directly affecting antibody binding. We confirmed this using a newly developed virion binding system. So, H655Y must be affecting a late entry step, but this shouldn’t make sense, 4/9

Hoping for insights, we next looked for natural adaptations that affected stem-helix antibody neutralization. Paradoxical to strong antibody selections for S adaptations, Omicron BA.1 S had become more sensitive to these antibodies, and it traced to, surprise surprise, H655Y! 3/9

…by ACCIDENT! We were testing stem-helix antibodies, cool because they cross-neutralize βCoVs by binding to not the variable receptor-binding S cap, but the conserved S stalk. We first saw that they also didn’t affect S2’ proteolytic activation, a crucial step for #coronavirus entry. 2/9

Cannot agree more! 😁

Haha thanks! I’m still new on this platform…😅