The diabetogenic mouse MHC class II molecule I-Ag7 is endowed with a switch that modulates TCR affinity
Kenji Yoshida, Adam L. Corper, Rana Herro, Bana Jabri, Ian A. Wilson, Luc Teyton
Kenji Yoshida, Adam L. Corper, Rana Herro, Bana Jabri, Ian A. Wilson, Luc Teyton
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Research Article

The diabetogenic mouse MHC class II molecule I-Ag7 is endowed with a switch that modulates TCR affinity

Abstract

Genetic susceptibility to autoimmunity is frequently associated with specific MHC alleles. Diabetogenic MHC class II molecules, such as human HLA-DQ8 and mouse I-Ag7, typically have a small, uncharged amino acid residue at position 57 of their β chain (β57); this results in the absence of a salt bridge between β57 and Argα76, which is adjacent to the P9 pocket of the peptide-binding groove. However, the influence of Argα76 on the selection of the TCR repertoire remains unknown, particularly when the MHC molecule binds a peptide with a neutral amino acid residue at position P9. Here, we have shown that diabetogenic MHC class II molecules bound to a peptide with a neutral P9 residue primarily selected and expanded cells expressing TCRs bearing a negatively charged residue in the first segment of their complementarity determining region 3β. The crystal structure of one such TCR in complex with I-Ag7 bound to a peptide containing a neutral P9 residue revealed that a network of favorable long-range (greater than 4 Å) electrostatic interactions existed among Argα76, the neutral P9 residue, and TCR, which supported the substantially increased TCR/peptide-MHC affinity. This network could be modulated or switched to a lower affinity interaction by the introduction of a negative charge at position P9 of the peptide. Our results support the existence of a switch at residue β57 of the I-Ag7 and HLA-DQ8 class II molecules and potentially link normal thymic TCR selection with abnormal peripheral behavior.

Authors

Kenji Yoshida, Adam L. Corper, Rana Herro, Bana Jabri, Ian A. Wilson, Luc Teyton

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Figure 9

SPR affinity measurements between TCR/pMHC.

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SPR affinity measurements between TCR/pMHC. (A) Affinity measurements of...
(A) Affinity measurements of TCR 21.30 for I-Ag7HEL11–27 and I-Ag7HEL11–279E (top) and TCR 21.30 CDR3β 109 D → G and I-Ag7HEL11–27 (bottom) (pMHC molecules were injected at 5, 2.5, 1.25, 0.625, 0.312, and 0.187 μM over immobilized TCR). Sensorgrams represent specific binding after subtraction of control (I-Ag7 2.5mi) and were fitted using global analysis with the BIAcore software using a 1:1 Langmuir model (residuals are shown below the sensorgrams). Overlays are at 5 μM. (B) SPR measurement of the affinity of recombinant TCR 21.30 for I-Ag7HEL11–27 and I-Ag7 β57 S → D HEL11–27. TCR was immobilized on a CM5 chip (1200 RUs), and pMHC molecules were injected at 2 μM concentration. Sensorgrams presented in the figure are the subtraction of the experimental trace minus the negative control (I-Ag7 2.5mi). (C) Electrostatic surfaces of I-Ag7HEL11–27 (left) and TCR 21.30 (right) showing charge complementarity between the 2 surfaces. TCR has been “peeled off” the MHC (180° rotation) to reveal the interacting surfaces. The corresponding positive (pMHC, blue) and negative (TCR, red) surfaces are circled. Positive charge is contoured blue, while negative charge is red (–5 to +5 kT/e). (D) Effect of increasing salt concentrations on the binding of I-Ag7HEL11–27 (black) and I-Ag7HEL11–279E (red) to TCR 21.30. I-Ag7HEL11–27 was injected at 2 μM and I-Ag7HEL11–279E at 8 μM with increasing NaCl concentrations (150, 175, 200, 225, and 250 mM NaCl). Sensorgrams are double subtractions (control pMHC and buffer). Kinetic on (squares or upside-down trangles) and off rates (triangles or diamonds) are plotted relative to physiological ionic conditions (150 mM). Representative experiments are presented (n = 5).