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. LAMTOR1 is 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. Involved in the control of embryonic stem cells differentiation; together with FLCN it is necessary to recruit and activate RRAGC/RagC and RRAGD/RagD at the lysosomes, and to induce exit of embryonic stem cells from pluripotency via non-canonical, mTOR-independent TFE3 inactivation (By similarity). Part of the Ragulator complex composed of LAMTOR1, LAMTOR2, LAMTOR3, LAMTOR4 and LAMTOR5 (PubMed:20381137, PubMed:22980980). LAMTOR4 and LAMTOR5 form a heterodimer that interacts, through LAMTOR1, with a LAMTOR2, LAMTOR3 heterodimer (PubMed:20381137, PubMed:22980980). Interacts with LAMTOR2 and LAMTOR3; the interaction is direct (PubMed:20381137, PubMed:22980980). 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 (PubMed:20381137, PubMed:22980980). The Ragulator complex interacts with SLC38A9; the probable amino acid sensor (PubMed:25561175, PubMed:25567906). 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 (PubMed:31704029, PubMed:31672913). Interacts with RRAGB and RRAGD; the interaction is direct indicating that it probably constitutes the main RAG-interacting subunit of the Ragulator complex (PubMed:22980980). Interacts with MMP14 (PubMed:19654316). Interacts with CDKN1B; prevents the interaction of CDKN1B with RHOA leaving RHOA in a form accessible to activation by ARHGEF2 (PubMed:19654316). Interacts with PIP4P1 (PubMed:29644770). Down-regulated by cholesterol (at protein level). Belongs to the LAMTOR1 family.