Fig. 1: Identification of the PBM of Mylu-B*67:01 and display of the MQQPW insertion pattern and peptide-binding structural basis in the pMylu-B*67:01-P1 structure.

a The in vitro refolding results of Mylu-B*67:01 with the R9Ps are elucidated through gel filtration chromatograms. The chromatographic profile indicates that the peak for the target complex is anticipated to be observed near the 100 ml mark on a Superdex 200 Big Gel Filtration Chromatography column. b The PBM of Mylu-B*67:01 determined by RPLD-MS. Sequence logo created using icelogo software shows the AA-weighted probability of binding R9Ps at each position of type Shannon. c The in vitro refolding results of Mylu-B*67:01 with three COVID-19 peptides (P1, P2, and P3) as shown in the gel filtration chromatogram. All three peptides were screened from the spike protein based on the PBM of Mylu-B*67:01.The sample destination peak should appear near 16 ml on a superdex 200 small gel filtration chromatography column. d The overall structure of pMylu-B*67:01-P1 and the electron density map highlighting the significant residues and the bound peptide. pMylu-B*67:01-P1 is composed of the alpha chain (HC), β2m and the peptide. The insertion sequence MQQPW is displayed in red, with a black arrow indicating the location of the 3₁₀ helix. The peptide, inserted MQQPW, D61 and R67 are shown in stick form, and their unbiased 2Fo-Fc electron density maps are also shown. The contour level for the unbiased 2Fo-Fc electron density map is set at 1.0 sigma. e Charged surface and residue composition of the PBG of pMylu-B*67:01-P1. Six pockets marked in red with P7-H sticking out of the PBG. D61 and R67 are bolded to indicate their significance. f Structure and sequence comparison of the B pocket of Mylu-B*67:01 with other B pockets that prefer to accommodate P2-P, with key P71 and P72 residues marked with red stars. g Structure and sequence comparison of the F pocket of Mylu-B*67:01 with other similar F pockets, where key P86, P100 and P121 residues were marked with red stars.