PROSITE documentation PDOC00428
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.

Last update:

April 2006 / Pattern revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

COBALAMIN_BINDING, PS00468; Eukaryotic cobalamin-binding proteins signature  (PATTERN)


1AuthorsSeetharam B. Alpers D.H.
TitleAbsorption and transport of cobalamin (vitamin B12).
SourceAnnu. Rev. Nutr. 2:343-369(1982).
PubMed ID6313022

2AuthorsPlatica O. Janeczko R. Quadros E.V. Regec A. Romain R. Rothenberg S.P.
TitleThe cDNA sequence and the deduced amino acid sequence of human transcobalamin II show homology with rat intrinsic factor and human transcobalamin I.
SourceJ. Biol. Chem. 266:7860-7863(1991).
PubMed ID1708393

3AuthorsLi N. Seetharam S. Lindemans J. Alpers D.H. Arwert F. Seetharam B.
TitleIsolation and sequence analysis of variant forms of human transcobalamin II.
SourceBiochim. Biophys. Acta 1172:21-30(1993).
PubMed ID8439564

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