Fig. 1: Structures of SIDT1 and SIDT2 homodimer and their pH-dependent RNA-binding and oligomerization.

a Overall cryo-EM maps and structure models of SIDT1 and SIDT2. Protomers A and B of SIDT1 are colored in light blue and deep blue, respectively. They are colored in light green and deep green for SIDT2, respectively. b Detailed dimeric interactions of ECD1 and ECD2 between two SIDT1 protomers. Potential hydrophobic interacting residues are shown as sticks. Potential hydrogen bonds are represented as yellow dashed lines. c Comparison of dimer interface of the TMDs between SIDT1 and SIDT2. d High-resolution confocal images of the BiFC assay for SIDT1 (FL full-length, top; TMD, bottom) fused to the N-terminal and C-terminal fragments of GFP fluorescent protein. DAPI (blue) was used for nuclear staining. Scale bar, 20 µm. e EMSA results of SIDT1^ECD-Dimer under pH 5.5 and pH 8.0 conditions. Final protein concentrations in lanes 1–5 are 0, 1, 2, 3, and 4 μM, respectively, and final concentrations of the 5’-FAM-labeled small RNAs are 2.5 μM in each lane. Bound, protein-RNA complexes; Unbound, free RNA. f MST analysis measuring binding affinities of SIDT1^ECD and SIDT1^ECD-Dimer with small RNAs across different pH conditions. The calculated dissociation constant (K_D) value represents affinity between SIDT1^ECD or SIDT1^ECD-Dimer with miRNAs. MST results are representative of three independent experiments. SEC (left panel) and SV-AUC (right panel) analyses of SIDT1^ECD-Dimer (g) and SIDT1^ECD (h) forming complexes with dsmiR168a, respectively. Experiments were performed at pH 5.5. Experiments were conducted twice. Data represent means ± s.d.