Possible role in regulating endocytosis of the transferrin receptor at the plasma membrane. Alternatively, may function as a negative regulator of the amino acid-induced TOR signaling by inhibiting the formation of active Rag GTPase complexes. Preferentially binds inactive Rag GTPase complexes and prevents their interaction with the mTORC1 complex inhibiting its relocalization to lysosomes and its activation. Thereby, may indirectly regulate cell growth, proliferation and autophagy (By similarity). Homodimer or homooligomer. Specifically associated with transferrin receptor-containing clathrin-coated pits and clathrin-coated vesicles. May also localize to the nucleus (By similarity). The SH3 domain mediates localization to the clathrin-coated pits and vesicles. Contaminating sequence. Potential poly-A sequence.