Lysosomal cobalamin transport escort protein LMBD1 (LMBD1)

Lysosomal cobalamin transport escort protein LMBD1 (encoded by the LMBRD1 gene) is a **lysosomal membrane transporter** essential for the export of vitamin B12 (cobalamin) from lysosomes to the cytosol, enabling its conversion to metabolic cofactors adenosylcobalamin and methylcobalamin[1][4][6][7]. These cofactors are crucial for methylmalonyl-CoA mutase and methionine synthase activity, supporting amino acid, lipid, and cholesterol metabolism. LMBD1 also acts as an **adapter protein** mediating the internalization and clathrin-mediated endocytosis of the insulin receptor, thereby regulating insulin signaling[1][2][6][7]. Mutations in LMBRD1 cause methylmalonic acidemia with homocystinuria (cblF type), leading to multisystem disease. An isoform of LMBD1 (NESI) interacts with hepatitis delta antigen, potentially aiding viral assembly. LMBD1 is widely studied as a disease gene and transporter, but no direct drugs target the protein itself; molecular diagnosis and B12 supplementation are standard interventions in deficiency states[1][2].

Other names

LMBRD1LMBR1 domain containing 1C6orf209NESIBM-021CD001MSTP044FLJ11240bA810I22.1cblFHDAg-L-interacting protein NESIhepatitis delta antigen-L interacting proteinliver regeneration p-53 related proteinnuclear export signal-interacting proteinMAHCFprobable lysosomal cobalamin transporter

Vitamin B12 supplementation: bypasses defective lysosomal export, restoring B12 bioavailability