eLife Assessment
The manuscript by Rotsides et al. reports the design and validation of SMART-MR1, a miniaturized MR1 metabolite-display platform in which the α1/α2 ligand-binding domain is stabilized by a synthetic helical domain in place of the α3 domain and β2-microglobulin. Supported by biochemical, biophysical, and structural approaches, including ITC, NMR, and cryo-EM, the work provides solid evidence that SMART-MR1 retains native-like ligand binding and A-F7 TCR recognition while enabling experimental approaches for ligand screening that are difficult with conventional MR1 constructs. The study is valuable for the MR1 and MAIT-cell fields, particularly as a tool for ligand screening and mechanistic studies of MR1-restricted antigen presentation. There are several suggestions to further strengthen the study's impact, including clearer benchmarking against existing MR1 platforms, broader validation across ligands and TCRs, and functional evidence from MAIT-cell staining or activation assays.