Fig. 3: Multiple conformations of μ4-CTD in the AP-4 core and AP-4/ARF1 complexes.

a Superimposition of the atomic models of the AP-4 core and AP-4/ARF1 complexes in the μ4-CTD-docked and μ4-CTD-undocked states, respectively. In the μ4-CTD-docked state, the root-mean-square deviation (RMSD) is 0.76 Å across backbone atoms (left panel). In the μ4-CTD-undocked state, the RMSD is 1.38 Å across backbone atoms (right panel). b, c Single-molecule FRET (smFRET) distribution histograms of Cy3/Cy5-labeled AP-4 core-His₁₀ in the soluble form (b) and ARF1-bound form (c). The left panels show the FRET efficiency distributions, revealing a high FRET population (peaked at E = 0.8), alongside a relatively broad distribution of lower FRET values (E < 0.3). The red curves represent probability distribution analysis (PDA) fits. The right panels depict the corresponding distance distributions between the labeled sites derived from the smFRET data. Source data are provided as a Source Data file. d A schematic diagram of the dynamic conformational states of the AP-4 core and AP-4/ARF1 complexes based on SWISS-MODEL (PDB templates: 9U9J; 9C5B; 6QH6) and smFRET results. The distance of the geometric centers between the two His₁₀ tags, along with the fluorescence-labeling sites in μ4-CTD and ε are labeled. All subunits are colored with the same color scheme in Fig. 2a.