Cobalamin transport proteins (Cbl transport proteins)

Cobalamin transport proteins are a specialized group of glycoproteins and receptors that facilitate the absorption, systemic circulation, and cellular uptake of Vitamin B12 (cobalamin), an essential cofactor for DNA synthesis and fatty acid metabolism [1.2.2, 1.3.3]. The process involves three primary binding proteins: haptocorrin (TCN1), which protects B12 from gastric acid; gastric intrinsic factor (GIF), which binds B12 in the duodenum and mediates its absorption in the terminal ileum via the cubam receptor; and transcobalamin II (TCN2), which transports B12 through the blood to tissues for uptake via the CD320 receptor [1.3.2, 1.4.4]. Dysfunction or deficiency in these proteins, such as the loss of intrinsic factor in pernicious anemia, leads to severe B12 deficiency, megaloblastic anemia, and irreversible neurological damage [1.2.3, 1.4.3]. These proteins are therapeutic targets for B12 supplementation and are also being explored for targeted drug delivery, particularly in cancer therapy, due to the high expression of transcobalamin receptors in rapidly dividing cells [1.5.1, 1.5.2]. Common medications like metformin and proton pump inhibitors can interfere with these transport proteins, necessitating monitoring of B12 status [1.6.1, 1.6.5].

Other names

Intrinsic factor and other cobalamin transport proteinsVitamin B12 transport proteinsCobalamin binding proteinsGastric intrinsic factorHaptocorrinTranscobalaminR-binderTranscobalamin ITranscobalamin II

Drugs targeting these proteins primarily act as exogenous replacements (cobalamins) that utilize the transport system for absorption and cellular delivery, or as inhibitors (e.g., metformin, PPIs) that interfere with the binding or acidic environment required for protein-cobalamin complex formation [1.6.1, 1.6.5].