 Before Rag-GTPases can bind to the Ragulator, Rag A/B must be GTP loaded via guanine nucleotide exchange factors (GEFs), and RAG C/D must be GDP loaded.Once Rag-GTPases are bound to the regulator complex, the mTORC1 can be translocated to the surface of the lysosome.At the lysosomal surface, the mTORC1 will then bind to Rheb, but only if Rheb was first loaded to a GTP via GEFs.