Fig. 2: B6 targets a linear epitope in the coronavirus S₂ fusion machinery.

a,b, Molecular surface representation of a composite model of the B6-bound MERS-CoV S cryo-EM structure and of the B6-bound MERS-CoV S stem helix peptide crystal structure shown from the side (a) and viewed from the viral membrane (b). MERS-CoV S protomers are colored pink, cyan and gold, and the B6 Fab heavy and light chains are colored purple and magenta, respectively. The composite model was generated by docking the crystal structure of B6 bound to the MERS-CoV S stem helix into the cryo-EM map. c, Identification of a conserved 15-residue sequence spanning the stem helix. Residue numberings for MERS-CoV S and SARS-CoV-2 S are indicated on the top and bottom of the alignment, respectively. Sequence alignment was performed using Multalin¹⁰³ and visualized using ESPript3.0 (ref. ¹⁰⁴). d,e, Binding of 0.1 µM B6 mAb (d) or 1 µM B6 Fab (e) to biotinylated coronavirus S stem helix peptides immobilized at the surface of biolayer interferometry biosensors. Control: no peptide immobilized. One representative example of two independent experiments with three technical replicates is shown.