Fig. 4. Molecular interactions at chaperone-client interfaces affect MHC I surface expression.

a Cartoon representation of the chaperone complex as shown in Fig. 1c. The components tapasin, MHC I hc and β₂m are displayed in orange, teal and green, respectively. Regions magnified in b–e are indicated by dashed boxes. ERp57 is not shown for the sake of clarity. Transmembrane helices and C-terminal regions (C) of MHC I hc and tapasin are indicated schematically. b Zoom-in of the α2-1 helix region of MHC I and tapasin. Interface residues forming hydrogen bonds (black dashed lines) are shown as sticks. c Magnification of the interface formed between the β hairpin of tapasin and the α1/α2 domains of MHC I. d Close-up view of the C-terminal domain of tapasin and the α3 domain of MHC I. e Interface formed between β₂m and the IgC domain of tapasin. f Restored MHC I surface expression of tapasin-deficient HAP1 cells by interface mutants of tapasin as assessed by flow cytometry. Mean fluorescence intensities of cells stained with APC-conjugated pan-HLA-A/B/C-specific antibody (W6/32) were normalized to the tapasin amount of the wildtype (dark gray, upper dashed line) (±SD, n = 4 biologically independent samples; Q261A, R333E/S336Y, and E307A, n = 3 biologically independent samples; mock transfected, n = 2 biologically independent samples). The lower dashed line represents the level of MHC I surface expression of mock-transfected cells (white). The gating strategy is displayed in Supplementary Fig. 8. α2-1 interface, brown; β-hairpin interface, dark orange; α3 interface, orange; β₂m interface, light orange. WT wildtype, − mock transfected. Source data for e are provided as a Source Data file. The same color code as used in a is applied in b–e.