TBC1D13 is a GTPase-activating protein (GAP) that specifically regulates RAB35, a small GTPase involved in intracellular trafficking. Its primary function is to catalyze GTP hydrolysis on RAB35, converting it to its inactive GDP-bound state 1. TBC1D13 plays a crucial role in insulin-stimulated glucose transporter GLUT4 translocation to the plasma membrane in adipocytes. When TBC1D13 is overexpressed, it inhibits insulin-stimulated GLUT4 translocation by inactivating RAB35; conversely, constitutively active RAB35 can bypass this inhibition 1. TBC1D13 functions as part of a larger regulatory network where Retromer acts as a hub for coordinating RAB GTPase switching, recruiting TBC1D13 to regulate retrieval sub-domain function in endosomal recycling 2. TBC1D13 is part of an Akt-targeted family of RAB GAPs (TBC1D1, TBC1D4, TBC1D13) that regulate multiple RAB GTPases downstream in insulin signaling pathways controlling GLUT4 trafficking 3. Dysregulation of TBC1D13 may have disease implications, as it has been identified as a tumor-associated antigen with autoantibodies detected in hepatocellular carcinoma patients 4, suggesting potential roles in cancer-related metabolic alterations.