MFSD1 (major facilitator superfamily domain containing 1) is a lysosomal membrane transporter that functions as a general dipeptide uniporter. Working as a heteromeric complex with its accessory subunit GLMP, MFSD1 selectively exports cationic dipeptides (containing lysine, arginine, or histidine residues) with net positive charge from the lysosomal lumen to the cytosol 12. The transport is highly selective, rejecting single amino acids, tripeptides, and anionic dipeptides 2. Structurally, MFSD1 contains 12 transmembrane domains characteristic of major facilitator superfamily transporters and can form homodimers; GLMP's luminal domain and N-glycosylation are essential for complex stabilization 3. Beyond dipeptide transport, MFSD1 participates in a larger protein complex with GIMAP5, which is critical for lymphocyte development and liver homeostasis; genetic disruption causes lymphopenia, splenomegaly, and liver pathology 4. MFSD1 expression is nutrient-responsive, upregulating during amino acid deprivation 5. Clinically, MFSD1 has emerged as a potential biomarker associated with hepatocellular carcinoma prognosis and Parkinson's disease diagnosis 67. Additionally, MFSD1 hypermethylation correlates with type 2 diabetes susceptibility in Han populations 8.