Awad Wael, Gherardin Nicholas A, Ciacchi Lisa, Keller Andrew N, Liu Ligong, Fairlie David P, McCluskey James, Godfrey Dale I, Rossjohn Jamie
Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria 3800, Australia.
Department of Microbiology and Immunology, The Peter Doherty Institute for Infection and Immunity at the University of Melbourne, Melbourne, Victoria 3000, Australia.
J Biol Chem. 2025 Jun 24:110416. doi: 10.1016/j.jbc.2025.110416.
Mucosal-associated invariant T (MAIT) cells express a TRAV1-2 T cell receptor (TCR) that recognises microbial vitamin B2-derivatives presented by the MHC class I-related molecule, MR1. Most MAIT TCRs incorporate a biased TCR-β repertoire, predominantly TRBV20-1 and TRBV6, but some utilise other TRBV genes, including TRBV28. A second conserved, albeit less frequent TRAV36 TRBV28 T cell population exhibits MAIT-like phenotypic features but use a markedly distinct mode of MR1-antigen-recognition compared to MAIT TCR-MR1 binding. Nevertheless, our understanding of how differing TCR gene usage results in altered MR1 binding modes remains incomplete. Here, binding studies demonstrated differential affinities and antigen-specificities between TRBV6 and TRBV28 MR1-restricted TCRs. Alanine-scanning mutagenesis on the TRAV36-TRBV28 TCR, revealed a strong dependence on germline-encoded residues within the highly selected CDR3α loop, similar to TRAV1-2- TRBV6 TCRs, and further alanine-scanning mutagenesis experiments demonstrate differential energetic footprints by these TCRs atop MR1. We determined the crystal structure of a MAIT TRAV1-2-TRBV28 TCR-MR1-5-OP-RU ternary complex. This structure revealed a docking mode conserved amongst other TRAV1-2 MAIT TCRs, with the TRBV28-encoded TCR-β chain adopting highly distinct docking modes between the TRAV1-2 and TRAV36 TCRs. This indicates that the TCR-α chain dictates the positioning and role of the TCR-β chain. Taken together, these findings provide new molecular insights into MR1-Ag driven selection of paired TCR-α and TCR-β chains.
黏膜相关恒定T（MAIT）细胞表达一种TRAV1-2 T细胞受体（TCR），该受体可识别由MHC I类相关分子MR1呈递的微生物维生素B2衍生物。大多数MAIT TCR包含偏向性的TCR-β谱系，主要为TRBV20-1和TRBV6，但也有一些利用其他TRBV基因，包括TRBV28。第二个保守的TRAV36-TRBV28 T细胞群体虽然频率较低，但表现出MAIT样的表型特征，不过与MAIT TCR-MR1结合相比，其使用明显不同的MR1抗原识别模式。然而，我们对不同TCR基因使用如何导致MR1结合模式改变的理解仍不完整。在这里，结合研究证明了TRBV6和TRBV28 MR1限制性TCR之间的亲和力和抗原特异性差异。对TRAV36-TRBV28 TCR进行丙氨酸扫描诱变，发现其对高度选择的CDR3α环内的种系编码残基有强烈依赖性，这与TRAV1-2-TRBV6 TCR相似，进一步的丙氨酸扫描诱变实验证明了这些TCR在MR1上的能量足迹差异。我们确定了MAIT TRAV1-2-TRBV28 TCR-MR1-5-OP-RU三元复合物的晶体结构。该结构揭示了一种在其他TRAV1-2 MAIT TCR中保守的对接模式，其中TRBV28编码的TCR-β链在TRAV1-2和TRAV36 TCR之间采用高度不同的对接模式。这表明TCR-α链决定了TCR-β链的定位和作用。综上所述，这些发现为MR1-抗原驱动的配对TCR-α和TCR-β链选择提供了新的分子见解。
