Fig. 3. A gatekeeper loop movement of 10 Å is induced upon ECSIT_CTER binding to ACAD9.

ECSIT binding to ACAD9 induces the deflavination of ACAD9 and the displacement of a loop bridging the ECSIT:FAD binding sites. A ACAD9_S191A in dehydrogenase form, with the bound FAD highlighted in yellow. The β1–β2 loop consisting of ACAD9 residues 178–195 is depicted in dark teal. B ACAD9_WT-ECSIT_CTER complex showing the location of the two ECSIT binding sites adjacent to ACAD9 residues F178-R195 in bold. C Close-up of (A), showing the loop adopting a downfacing position, in a closed conformation, acting as a barrier to the internal core of ACAD9 and the FAD pocket. D Close-up of (B), after ECSIT binds to ACAD9. Residue Gly186 is on the tip of the β1–β2 loop and is displaced by ~10 Å, flipping upwards into an open conformation. E Superposition of the β1–β2 loop in ACAD9 unbound (cyan) and in complex with ECSIT_CTER (dark teal). F Cα-Cα distance positions of the β1–β2 loop residues in ACAD9 unbound vs. in complex with ECSIT_CTER. Source data are provided as a Source Data file.