Acts as a guanine-nucleotide exchange factor (GEF). Promotes guanine-nucleotide exchange on ARF1, ARF3 and ARF6. Promotes the activation of ARF factors through replacement of GDP with GTP. The cell membrane form, in association with ARL4 proteins, recruits ARF6 to the plasma membrane (By similarity). Involved in neurite growth (By similarity). Heteromer. Composed of GRASP, CYTH2 and at least one GRM1. Interacts with ARRB1. Interacts with ARL4D; the interaction is direct (By similarity). Directly interacts with CCDC120 through the coiled coil domain; this interaction stabilizes CCDC120, possibly by preventing its ubiquitination, and is required for neurite growth in neuroblastoma cells. Interacts (via N-terminal domain) with INAVA (via N-terminal domain) (By similarity). Recruited to the cell membrane through its association with ARL4A, ARL4C and ARL4D. Requires also interaction with phosphoinositides for targeting to plasma membrane. In differentiating neuroblastoma cells, colocalizes with CCDC120 in both neurite shaft and growth cone areas. Binds via its PH domain to the inositol head group of phosphatidylinositol 3,4,5-trisphosphate. The PH domain is necessary and sufficient for plasma membrane relocalization (By similarity). Autoinhibited by its C-terminal basic region. The coiled coil domain is involved in interaction with CCDC120.