The dimer has GTPase activity; the active site contains residues from both subunits. Monomer in the presence of bound GDP and in the absence of bound nucleotide. Homodimer in the presence of bound GTP. Heterodimer with GIMAP2. Colocalizes with GIMAP2 on the surface of cytoplasmic lipid droplets. Most abundantly expressed in spleen, lymph nodes, and fetal kidney, but also present in the heart and the small intestine. Lower expression levels are found in lung, kidney, liver, and thyroid, salivary, and mammary glands. Also detected in the thymus (PubMed:15474311). Detected in T-cells (PubMed:23454188). Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. AIG1/Toc34/Toc159-like paraseptin GTPase family. IAN subfamily.