Involved in membrane trafficking via some guanine nucleotide exchange factor (GEF) activity and its ability to bind clathrin. Acts as a GEF for Arf and Rab, by exchanging bound GDP for free GTP. Binds phosphatidylinositol 4,5-bisphosphate, which is required for GEF activity. May also act as a E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with TSC2; interaction is inhibited by TSC1. Interacts with PKM, ARF1 and ARF6. Forms a ternary complex with clathrin heavy chain (CLTC) and HSPA1A. Recruited onto actin-rich surface protrusions. Widely expressed. The disease is caused by variants affecting the gene represented in this entry.