Fig. 3: The editing loop of tapasin contributes to a widened F-pocket of MHC I.

a Cartoon representation of the chaperone complex as shown in Fig. 1c. Tapasin, MHC I hc and β₂m are colored in orange, teal and green, respectively. Region magnified in b–d is indicated by a dashed box. ERp57 is not shown for the sake of clarity. b Side view onto the editing loop (stick representation) of tapasin with corresponding electron density map (contour level: 1.5 σ). Dashed lines represent hydrogen bonds or salt bridges. The same color code as in a is applied. hc heavy chain. c Top view onto the editing loop with corresponding electron density and color code as shown in b. d Close-up view into the F-pocket of MHC I with corresponding electron density and color code as displayed in b. e MHC I surface expression of tapasin-deficient HAP1 cells (white), expressing wildtype (WT, dark gray) or different interaction mutants of tapasin (orange). Flow cytometry was performed using an APC-conjugated pan-HLA-A/B/C-specific antibody (W6/32). The lower black dashed line represents the level of MHC I surface expression of cells transfected with a vector devoid of gene of interest. The upper black dashed line represents the level of MHC I surface expression of cells expressing wildtype tapasin. The mean fluorescence intensity of MHC I surface expression was normalized to wildtype tapasin (±SD; n = 4 biologically independent samples; K20E, n = 3 biologically independent samples; L18W and mock transfected, n = 2 biologically independent samples). The gating strategy is displayed in Supplementary Fig. 8. WT wildtype, − mock transfected. Source data for e are provided as a Source Data file.