Alternative titles; symbols
HGNC Approved Gene Symbol: TCN1
Cytogenetic location: 11q12.1 Genomic coordinates (GRCh38): 11:59,852,808-59,866,487 (from NCBI)
There are 3 human vitamin B12 (cobalamin)-binding proteins: gastric intrinsic factor (GIF; 609342); plasma transcobalamin II (TCN2; 613441); and transcobalamin I (TCN1), an R binder protein. R binder proteins are a class of immunologically identical but electrophoretically distinct glycoproteins found in many secretions, such as saliva, gastric juice, tears, milk, and leukocytes, and differ only in their carbohydrate content; 'R' denotes 'rapid,' referring to electrophoretic mobility (Azen and Denniston, 1979). Transcobalamin I is also found in neutrophils, where it is restricted to the secondary granules (Johnston et al., 1989).
Johnston et al. (1989) isolated and characterized full-length cDNA clones encoding the TCN1 gene from a human granulocyte cDNA library. The deduced 433-residue protein showed extensive areas of homology with rat gastric intrinsic factor, which implicated regions potentially important for vitamin B12 binding.
Johnston et al. (1992) determined that the TCN1 gene contains 9 exons. Comparison of the genomic structures of TCN1 and GIF suggested that the 2 genes arose by a gene duplication.
Yang-Feng et al. (1991) mapped the TCN1 gene to chromosome 11q11-q12 by in situ hybridization.
Azen and Denniston (1979) demonstrated genetic polymorphism of the vitamin B12-binding proteins. Data on gene frequencies of allelic variants were tabulated by Roychoudhury and Nei (1988).
Azen, E. A., Denniston, C. Genetic polymorphism of vitamin B12 binding (R) protein of human saliva detected by isoelectric focusing. Biochem. Genet. 17: 909-920, 1979. [PubMed: 540023] [Full Text: https://doi.org/10.1007/BF00504312]
Johnston, J., Bollekens, J., Allen, R. H., Berliner, N. Structure of the cDNA encoding transcobalamin I, a neutrophil granule protein. J. Biol. Chem. 264: 15754-15757, 1989. [PubMed: 2777761]
Johnston, J., Yang-Feng, T., Berliner, N. Genomic structure and mapping of the chromosomal gene for transcobalamin I (TCN1): comparison to human intrinsic factor. Genomics 12: 459-464, 1992. Note: Erratum: Genomics 14: 208 only, 1992. [PubMed: 1463480] [Full Text: https://doi.org/10.1016/0888-7543(92)90435-u]
Roychoudhury, A. K., Nei, M. Human Polymorphic Genes: World Distribution. New York: Oxford Univ. Press (pub.) 1988.
Yang-Feng, T. L., Berliner, N., Deverajan, P., Johnston, J. Assignment of two human neutrophil secondary granule protein genes, transcobalamin I and neutrophil collagenase to chromosome 11. (Abstract) Cytogenet. Cell Genet. 58: 1974 only, 1991.