{PDOC00636}
{PS00803; CALRETICULIN_1}
{PS00804; CALRETICULIN_2}
{PS00805; CALRETICULIN_REPEAT}
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* Calreticulin family signatures *
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Calreticulin [1] (also known as calregulin, CRP55 or HACBP) is a high-capacity
calcium-binding protein   which   is  present  in  most  tissues  and  located
at the  periphery  of the  endoplasmic (ER) and the sarcoplamic reticulum (SR)
membranes.  It probably plays a role in the storage of calcium in the lumen of
the ER and SR and  it  may  well have other important functions. Structurally,
calreticulin  is  a protein  of  about 400  amino  acid residues consisting of
three domains:

 a) An N-terminal, probably globular, domain  of about 180 amino acid residues
    (N-domain);
 b) A central domain  of about  70 residues (P-domain)  which  contains  three
    repeats of an acidic 17 amino acid motif. This region binds calcium with a
    low-capacity, but a high-affinity;
 c) A C-terminal domain rich in acidic residues and in lysine (C-domain). This
    region binds calcium with a high-capacity but a low-affinity.

Calreticulin is evolutionary related to the following proteins:

 - Onchocerca volvulus antigen RAL-1. RAL-1 is highly similar to calreticulin,
   but  possesses  a  C-terminal  domain rich in lysine and arginine and lacks
   acidic residues  and  is  therefore  not  expected  to bind calcium in that
   region.
 - Calnexin   [2].   A  calcium-binding  protein  that  interacts  with  newly
   synthesized glycoproteins  in the endoplasmic reticulum. It seems to play a
   major role  in  the quality control apparatus of the ER by the retention of
   incorrectly folded proteins.
 - Calmegin  [3]  (or  calnexin-T),  a testis-specific calcium-binding protein
   highly similar to calnexin.

We developed three signature  patterns for  this family of proteins. The first
two patterns are based on conserved regions in the N-domain; the third pattern
corresponds to positions 4 to 16 of the repeated motif in the P-domain.

-Consensus pattern: [KRHN]-x-[DEQN]-[DEQNK]-x(3)-C-G-G-[AG]-[FY]-[LIVM]-[KN]-
                    [LIVMFY](2)
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: [LIVM](2)-F-G-P-D-x-C-[AG]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: [IVM]-x-[DV]-x-[DENST]-x(2)-K-P-[DEH]-D-W-[DEN]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2004 / Pattern and text revised.

[ 1] Michalak M., Milner R.E., Burns K., Opas M.
     "Calreticulin."
     Biochem. J. 285:681-692(1992).
     PubMed=1497605
[ 2] Bergeron J.J.M., Brenner M.B., Thomas D.Y., Williams D.B.
     "Calnexin: a membrane-bound chaperone of the endoplasmic reticulum."
     Trends Biochem. Sci. 19:124-128(1994).
     PubMed=8203019
[ 3] Watanabe D., Yamada K., Nishina Y., Tajima Y., Koshimizu U.,
     Nagata A., Nishimune Y.
     "Molecular cloning of a novel Ca(2+)-binding protein (calmegin)
     specifically expressed during male meiotic germ cell development."
     J. Biol. Chem. 269:7744-7749(1994).
     PubMed=8126001

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