RRAGB (Ras related GTP binding B) is a guanine nucleotide-binding protein that functions as a critical regulator of mTORC1 signaling in response to amino acid availability. RRAGB forms heterodimeric Rag complexes with RagC or RagD, cycling between inactive GDP-bound and active GTP-bound conformations 1. When GTP-bound, RRAGB promotes mTORC1 recruitment to lysosomes and subsequent activation by RHEB, thereby regulating global protein synthesis and metabolic responses to nutrient status 12. Mechanistically, RRAGB interacts with the Ragulator complex at the lysosomal membrane to transduce amino acid signals 2. During lysosomal damage, RRAGB-mediated mTORC1 inactivation occurs through the Ragulator-RRAGA-RRAGB complex, coordinating stress responses with stress granule formation 2. Clinically, dysregulated RRAGB expression is implicated in multiple pathologies. In glioblastoma, reduced RRAGB expression correlates with poor prognosis, while RRAGB restoration suppresses tumor growth through PI3K/AKT pathway inhibition 3. In diabetic kidney disease, elevated circMRP4-mediated RRAGB upregulation activates mTORC1 signaling, promoting podocyte apoptosis 4. Conversely, in colorectal cancer, circEXOC6B antagonizes HIF1A-RRAGB-mTORC1 feedback loops, suppressing tumor progression 5. These findings establish RRAGB as a potential therapeutic target across cancer and metabolic disease contexts.