Vitamin B12 transporter (No universal abbreviation; for human, TC (Transcobalamin) is common, for bacteria, BtuB or CbrT may apply)

The Vitamin B12 transporter refers to a functional family of proteins involved in the binding, absorption, and cellular delivery of vitamin B12 (cobalamin). In mammals, this includes three main binding proteins: haptocorrin, intrinsic factor, and transcobalamin, each with dedicated roles during gastrointestinal absorption and systemic transport. These proteins facilitate B12 uptake via high-affinity receptor binding and transport across epithelial barriers. In bacteria, notably E. coli, BtuB is an outer membrane TonB-dependent transporter, while ECF-type transporters like CbrT enable ATP-dependent uptake. Structural features include specialized binding pockets, domain motions, and conformational changes upon substrate interaction, with significant conservation and specificity for cobalamin analogues. Defects or inhibition of these transporters are implicated in B12 deficiency syndromes and their molecular diversity is exploited for targeted drug delivery and diagnostic approaches.

Other names

Transcobalamin (TC, mainly human/mammalian)Haptocorrin (HC)Intrinsic factor (IF)BtuB (bacterial, E. coli)ECF-CbrT (bacterial, Lactobacillus)Vitamin B12-binding proteinCobalamin transporter

Receptor-mediated endocytosis of B12 complexes (via IF-cubam, TC receptors, etc.); Energy-dependent translocation (ATPase activity in ABC/ECF systems); Ligand binding and conformational changes or domain motions facilitating substrate release