LAMTOR4 (late endosomal/lysosomal adaptor, MAPK and mTOR activator 4) is a critical component of the pentameric Ragulator complex that functions as a lysosomal scaffold for amino acid sensing and mTORC1 activation 1. The protein plays an essential role in stabilizing the Ragulator complex assembly, where the HBXIP-LAMTOR4 dimer acts as a nucleator that binds and stabilizes p18, allowing subsequent binding of other subunits 1. Structurally, LAMTOR4 forms a roadblock domain protein pair with LAMTOR5, with extensive hydrophobic interactions mediated by Lamtor1 2. The complex serves dual functions: acting as a guanine nucleotide exchange factor for Rag GTPases and recruiting them to the lysosomal membrane, ultimately leading to mTORC1 recruitment and activation in response to amino acid availability. LAMTOR4 expression is clinically significant, being elevated in various cancers including prostate cancer, where high expression correlates with poor survival outcomes 3. In hepatocellular carcinoma, LAMTOR4 upregulation is associated with mTOR signaling activation and worse prognosis 4. Additionally, LAMTOR4 shows differential requirements under fed versus starved conditions and exhibits synthetic-sick interactions with tumor suppressor folliculin, suggesting potential therapeutic targets 5.