Molecular characterization of the Rab1A-binding site on CALCOCO1 and OPTN. (A) Structure of the Rab1A:GTP:Mg²⁺:CALCOCO1 complex formed by two copies of CALCOCO1 and one copy of Rab1A as predicted by AlphaFold 3, with accompanying PAE plot. (B) Sulfo-NHS-diazirine (SDA) interprotein cross-links (green dashed lines) mapped onto the predicted structure of the Rab1A–CALCOCO1 complex. (C) The contact interface between Rab1A and the CALCOCO1 dimer, showing ChimeraX calculated contact residues of CALCOCO1 mediating the binding interface (red labels). (D) Structure of the Rab1A:GTP:Mg²⁺:OPTN complex formed by two copies of OPTN and one copy of Rab1A as predicted by AlphaFold 3, with accompanying PAE plot. (E) SDA interprotein cross-links (green dashed lines) mapped onto the predicted structure of the Rab1A–OPTN complex. (F) Magnified image of the contact interface between Rab1A and the OPTN dimer, showing ChimeraX calculated contact residues of OPTN mediating the binding interface (orange labels).