{PDOC00428}
{PS00468; COBALAMIN_BINDING}
{BEGIN}
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* Eukaryotic cobalamin-binding proteins signature *
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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]-[VT]-D-T-[GAME]-A-[LIVM]-[AV]-x-[LM]-A-[LIVMF]-[ST]-C
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: April 2006 / Pattern revised.

[ 1] Seetharam B., Alpers D.H.
     "Absorption and transport of cobalamin (vitamin B12)."
     Annu. Rev. Nutr. 2:343-369(1982).
     PubMed=6313022; DOI=10.1146/annurev.nu.02.070182.002015
[ 2] Platica O., Janeczko R., Quadros E.V., Regec A., Romain R.,
     Rothenberg S.P.
     "The cDNA sequence and the deduced amino acid sequence of human
     transcobalamin II show homology with rat intrinsic factor and human
     transcobalamin I."
     J. Biol. Chem. 266:7860-7863(1991).
     PubMed=1708393
[ 3] Li N., Seetharam S., Lindemans J., Alpers D.H., Arwert F., Seetharam B.
     "Isolation and sequence analysis of variant forms of human
     transcobalamin II."
     Biochim. Biophys. Acta 1172:21-30(1993).
     PubMed=8439564

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