May act as a GTPase-activating protein for Rab family protein(s). May play a role in the cell cycle and differentiation of various tissues. Involved in the trafficking and translocation of GLUT4-containing vesicles and insulin-stimulated glucose uptake into cells. Interacts with APPL2 (via BAR domain); interaction is dependent of TBC1D1 phosphorylation at Ser-229; interaction diminishes the phosphorylation of TBC1D1 at Thr-590, resulting in inhibition of SLC2A4/GLUT4 translocation and glucose uptake. Expressed in highest levels in hematopoietic cells, testis and kidney. Insulin-stimulated phosphorylation by AKT family kinases stimulates SLC2A4/GLUT4 translocation. Extended N-terminus.