Fig. 6. NMR mapping of the HLA-epitope interface reveals consistency between the pMHC crystal structure and its conformation in solution.

a Plot of scaled chemical shift changes (CSP) versus residue number between ¹⁵N-TROSY spectra of pMLL_747–755/HLA-B*0702 and MLL_747–755/HLA-B*0702 complexes. The line at CSP = 0.043_ppm indicates a threshold at 1δ over mean CSP. The four amino acid clusters, #1 (58–62), #2 (66-77), #3 (152–156) and #4 (167–173) with highest CSP values are outlined. b Zoomed-in view of the overlay of ¹⁵N-TROSY spectra of pMLL_747–755/HLA-B*0702 (green) and MLL_747–755/HLA-B*0702 complexes (blue) showing CSPs of residues (indicated by the arrows) belonging to clusters #2 and #3. c Cartoon view of the two alpha helices involved in epitope binding: NMR cluster #1 surrounding Arg₆₂ (orange), NMR cluster #2 surrounding Ile₆₆ (orange), NMR cluster #3 around Gln₁₅₅ (orange), and NMR cluster #4 near Glu-P₁ (blue). The peptide is shown as gray sticks, and pSer-P₄ is presented as a space-filling model. The minor alternate conformation for pSer-P₄ was omitted for clarity. d Overlay of pMHC structures with pMLL_747–755 (carbons are gray) and MLL_747–755 (carbons are yellow). The carbon atoms in HLA-B*0702 are colored in blue (with pMLL_747–755) or yellow (with MLL_747–755), respectively. The dashed lines show H-bonds between pMLL_747–755 and HLA residues. The arrowheads indicate the AA residues, NMR spectra of which can be affected by neighbors, explaining the reason for peaks clustering observed in (a).