As part of the Ragulator complex it is involved in amino acid sensing and activation of mTORC1, a signaling complex promoting cell growth in response to growth factors, energy levels, and amino acids. Activated by amino acids through a mechanism involving the lysosomal V-ATPase, the Ragulator functions as a guanine nucleotide exchange factor activating the small GTPases Rag. Activated Ragulator and Rag GTPases function as a scaffold recruiting mTORC1 to lysosomes where it is in turn activated. Adapter protein that enhances the efficiency of the MAP kinase cascade facilitating the activation of MAPK2 (By similarity). Part of the Ragulator complex composed of LAMTOR1, LAMTOR2, LAMTOR3, LAMTOR4 and LAMTOR5. LAMTOR4 and LAMTOR5 form a heterodimer that interacts, through LAMTOR1, with a LAMTOR2, LAMTOR3 heterodimer. Interacts with LAMTOR1 and LAMTOR3; the interaction is direct. The Ragulator complex interacts with both the mTORC1 complex and heterodimers constituted of the Rag GTPases RRAGA, RRAGB, RRAGC and RRAGD; regulated by amino acid availability. The Ragulator complex interacts with SLC38A9; the probable amino acid sensor (By similarity). Interacts with MAPK1 and MAP2K1 (By similarity). Component of the lysosomal folliculin complex (LFC), composed of FLCN, FNIP1 (or FNIP2), RRAGA/RagA or RRAGB/RagB GDP-bound, RRAGC/RagC or RRAGD/RagD GTP-bound, and Ragulator (By similarity). Belongs to the GAMAD family.