Extended Data Fig. 1: Structure of hSLC19A1 and distribution of critical mutations.

a, Cut-open side view (left), side view (middle), and cytosolic bottom view (right) of hSLC19A1‘s conservation surface mapping using ConSurf. The cytosolic entrance is indicated by dashed white oval. b, Extracellular top view of the hSLC19A1 inward-open structure, with extracellular loops and TM1/2/7/8 helices highlighted in red. c, Hydrophobic interactions of IL6-7 (aa 204–214) (salmon) with surrounding elements (grey). Key residues are shown as sticks and dots. d, Hydrogen bonding interactions of IL6-7 (aa 204–214) with surrounding elements. Key residues are shown as sticks and hydrogen bonds are represented as dashed lines. e,f, Effect of IL6-7 (aa 204-214) mutant on extracellular CDN signalling. 293T-STING cells were transfected with empty vector, WT hSLC19A1, or IL6-7 (aa 204–214) mutant, and followed by 2′3′-cGAMP stimulation or left untreated. Immunoblot analyses were carried out using the antibodies of IRF3, phospho-IRF3, STING, α-Tubulin and SLC19A1. Representative results from four independent experiments are shown. Data are mean ± s.e.m. of n = 4 independent experiments. **, p ≤ 0.01 by unpaired, two-tailed Student‘s t-test. For gel sorce data, see Supplementary Fig. 3. g, Distribution of previously proposed important residues of hSLC19A1, as well as hSLC19A1 mutations found in antifolate drug resistant cell lines and cancer patients (from BioMuta database with functional prediction probability >0.99). For the corresponding human residue number, references and study strategies, see Supplementary Table 2.