Rab geranylgeranyl transferase (RabGGT) catalyzes the addition of two geranylgeranyl groups to the C-terminal cysteine residues of Rab proteins, which is crucial for membrane association and function of these proteins in intracellular vesicular trafficking. This domain is inserted between pfam01239 repeats. This domain adopts an Ig-like fold and is thought to be involved in protein-protein interactions and might be involved in the recognition and binding of REP.