May act as a GTPase-activating protein (GAP) for Rab family protein(s). May act as a GAP for RAB7A. Can displace RAB7A and retromer CSC subcomplex from the endosomal membrane to the cytosol; at least retromer displacement seems to require its catalytic activity (PubMed:19531583, PubMed:20923837). Required for retrograde transport of cargo proteins from endosomes to the trans-Golgi network (TGN); the function seems to require its catalytic activity. Involved in regulation of autophagy (PubMed:22354992). May act as a molecular switch between endosomal and autophagosomal transport and is involved in reprogramming vesicle trafficking upon autophagy induction. Involved in the trafficking of ATG9A upon activation of autophagy. May regulate the recruitment of ATG9A-AP2-containing vesicles to autophagic membranes (PubMed:24603492). {ECO:0000269|PubMed:19531583, ECO:0000269|PubMed:20923837, ECO:0000269|PubMed:22354992, ECO:0000269|PubMed:24603492, ECO:0000305|PubMed:19531583, ECO:0000305|PubMed:22354992, ECO:0000305|PubMed:24603492}. This is the function of TBC1D5 (TBC1 domain family member 5, Ensembl gene identifier ENSG00000131374).