Fig. 3. The key residues at the SAM-binding site play a critical role in SAM binding and the interaction with GATOR1-KICSTOR.

(A) Interactions between SAM and the surrounding residues are shown in a ball-and-stick model (left) and a schematic diagram (right) in the structure of the SAM-bound MTase domain of dSAMTOR. (B) Structural comparison of the ligand-binding site of monomer A (left) and monomer B (right) in the V66W/E67P mutant dSAMTOR and the SAM-bound MTase domain of dSAMTOR. The color coding of each structure is shown above. (C) Co-IP assay to examine the interactions of Flag-hSAMTOR (WT and mutants) with HA-Nprl3 and Myc-Kaptin in the presence and absence of SAM. EV, empty vector. The assay was performed three times, which yielded similar results, and only the result of one representative experiment is shown.