PROSITE documentation PDOC00428Eukaryotic cobalamin-binding proteins signature
Description
In eukaryotes, a number of proteins are involved in the binding and transport of cobalamin (vitamin B12) [1]. Some of them have been sequenced and have been shown [2,3] to be evolutionary related and are listed below:
- Intrinsic factor (IF). The function of IF is to promote the absorption of cobalamin in the ileum by specific receptor-mediated endocytosis.
- Transcobalamin I (TC1) (also called R-binder protein). TC1 transports cobalamin from blood to cells.
- Transcobalamin II (TC2). TC2 transports cobalamin from blood to cells.
- Haptocorrin (cobalophilin). Haptocorrin binds to cobalamin and to cobalamin derivatives such as cobinamide. It may play a role in preventing the absorption of cobalamin analogues produced by bacteria.
These glycoproteins are polypeptides of about 400 amino acids that share many regions of similarity. As a signature pattern, we selected a highly conserved region in their central part.
Last update:April 2006 / Pattern revised.
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Technical section
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References
| 1 | Authors | Seetharam B. Alpers D.H. |
| Title | Absorption and transport of cobalamin (vitamin B12). | |
| Source | Annu. Rev. Nutr. 2:343-369(1982). | |
| PubMed ID | 6313022 | |
| DOI | 10.1146/annurev.nu.02.070182.002015 |
| 2 | Authors | Platica O. Janeczko R. Quadros E.V. Regec A. Romain R. Rothenberg S.P. |
| Title | The cDNA sequence and the deduced amino acid sequence of human transcobalamin II show homology with rat intrinsic factor and human transcobalamin I. | |
| Source | J. Biol. Chem. 266:7860-7863(1991). | |
| PubMed ID | 1708393 |
| 3 | Authors | Li N. Seetharam S. Lindemans J. Alpers D.H. Arwert F. Seetharam B. |
| Title | Isolation and sequence analysis of variant forms of human transcobalamin II. | |
| Source | Biochim. Biophys. Acta 1172:21-30(1993). | |
| PubMed ID | 8439564 |
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