Regulator of the TOR pathway, a signaling cascade that promotes cell growth in response to growth factors, energy levels, and amino acids. As part of the Ragulator complex, recruits the Rag GTPases and the mTORC1 complex to lysosomes, a key step in activation of the TOR signaling cascade by amino acids. Directly responsible for anchoring the Ragulator complex to membranes. Also required for late endosomes/lysosomes biogenesis it may regulate both the recycling of receptors through endosomes and the MAPK signaling pathway through recruitment of some of its components to late endosomes. May be involved in cholesterol homeostasis regulating LDL uptake and cholesterol release from late endosomes/lysosomes. May also play a role in RHOA activation. Part of the Ragulator complex composed of LAMTOR1, LAMTOR2 and LAMTOR3. Interacts with LAMTOR2 and LAMTOR3; the interaction is direct. The Ragulator complex interacts with both the mTORC1 complex and heterodimers of the Rag GTPases RRAGA, RRAGB, RRAGC and RRAGD. Interacts with RRAGB and RRAGD; the interaction is direct indicating that it probably constitutes the main RAG-interacting subunit of the Ragulator complex. Interacts with MMP14. Interacts with CDKN1B; prevents the interaction of CDKN1B with RHOA leaving RHOA in a form accessible to activation by ARHGEF2. Note: This description may include information from UniProtKB.