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- ***************************************************
- * Eukaryotic cobalamin-binding proteins signature *
- ***************************************************
-
- 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.
-
- -Consensus pattern: [SN]-V-D-T-[GA]-A-[LIVM]-A-x-L-A-[LIVMF]-T-C
- -Sequences known to belong to this class detected by the pattern: ALL.
- -Other sequence(s) detected in SWISS-PROT: NONE.
- -Last update: October 1993 / Pattern and text revised.
-
- [ 1] Seetharam B., Alpers D.H.
- Annu. Rev. Nutr. 2:343-369(1982).
- [ 2] Platica O., Janeczko R., Quadros E.V., Regec A., Romain R.,
- Rothenberg S.P.
- J. Biol. Chem. 266:7860-7863(1991).
- [ 3] Li N., Seetharam S., Lindemans J., Alpers D.H., Arwert F., Seetharam B.
- Biochim. Biophys. Acta 1172:21-30(1993).
-