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Calreticulin: Wikis


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PDB rendering based on 1hhn.
Available structures
1hhn, 1k91, 1k9c
Symbols CALR; FLJ26680; RO; SSA; cC1qR
External IDs OMIM109091 MGI88252 HomoloGene37911 GeneCards: CALR Gene
RNA expression pattern
PBB GE CALR 200935 at tn.png
PBB GE CALR 212953 x at tn.png
PBB GE CALR 214315 x at tn.png
More reference expression data
Species Human Mouse
Entrez 811 12317
Ensembl ENSG00000179218 ENSMUSG00000003814
UniProt P27797 Q3TVD2
RefSeq (mRNA) NM_004343 NM_007591
RefSeq (protein) NP_004334 NP_031617
Location (UCSC) Chr 19:
12.91 - 12.92 Mb
Chr 8:
87.73 - 87.74 Mb
PubMed search [1] [2]

Calreticulin is a multifunctional protein that binds Ca2+ ions (a second messenger molecule in signal transduction), rendering it inactive. The Ca2+ is bound with low affinity, but high capacity, and can be released on a signal (see inositol triphosphate). Calreticulin is located in storage compartments associated with the endoplasmic reticulum.

Calreticulin is also known as calregulin, CRP55, CaBP3 and calsequestrin-like protein. The term "Mobilferrin"[1] is considered to be the same as calreticulin by some sources.[2]



Calreticulin binds to misfolded proteins and prevents them from being exported from the Endoplasmic reticulum to the Golgi apparatus.

A similar quality-control chaperone, calnexin, performs the same service for soluble proteins as does calreticulin. Both proteins, Calnexin and calreticulin, have the function of binding to oligosaccharides containing terminal glucose residues, thereby targeting them for degradation. In normal cellular function, trimming of glucose residues off the core oligosaccharide added during N-linked glycosylation is a part of protein processing. If "overseer" enzymes note that residues are misfolded, proteins within the RER will re-add glucose residues so that other Calreticulin/Calnexin can bind to these proteins and prevent them from proceeding to the Golgi. This leads these aberrantly folded proteins down a path whereby they are targeted for degradation.


Transcription regulation

Calreticulin is also found in the nucleus, suggesting that it may have a role in transcription regulation. Calreticulin binds to the synthetic peptide KLGFFKR, which is almost identical to an amino acid sequence in the DNA-binding domain of the superfamily of nuclear receptors. The amino terminus of calreticulin interacts with the DNA-binding domain of the glucocorticoid receptor and prevents the receptor from binding to its specific glucocorticoid response element. Calreticulin can inhibit the binding of androgen receptor to its hormone-responsive DNA element and can inhibit androgen receptor and retinoic acid receptor transcriptional activities in vivo, as well as retinoic acid-induced neuronal differentiation. Thus, calreticulin can act as an important modulator of the regulation of gene transcription by nuclear hormone receptors.


Calreticulin binds to antibodies in certain sera of systemic lupus and Sjogren patients that contain anti-Ro/SSA antibodies. Systemic lupus erythematosus is associated with increased autoantibody titers against calreticulin, but calreticulin is not a Ro/SS-A antigen. Earlier papers referred to calreticulin as an Ro/SS-A antigen, but this was later disproven. Increased autoantibody titer against human calreticulin is found in infants with complete congenital heart block of both the IgG and IgM classes.[3]


Calreticulin has been shown to interact with Perforin[4] and NK2 homeobox 1.[5]


  1. ^ MeSH Mobilferrin
  2. ^ Beutler E, West C, Gelbart T (1997). "HLA-H and associated proteins in patients with hemochromatosis". Mol. Med. 3 (6): 397–402. PMID 9234244.  
  3. ^ "Entrez Gene: CALR calreticulin".  
  4. ^ Andrin, C; Pinkoski M J, Burns K, Atkinson E A, Krahenbuhl O, Hudig D, Fraser S A, Winkler U, Tschopp J, Opas M, Bleackley R C, Michalak M (Jul. 1998). "Interaction between a Ca2+-binding protein calreticulin and perforin, a component of the cytotoxic T-cell granules". Biochemistry (UNITED STATES) 37 (29): 10386–94. doi:10.1021/bi980595z. ISSN 0006-2960. PMID 9671507.  
  5. ^ Perrone, L; Tell G, Di Lauro R (Feb. 1999). "Calreticulin enhances the transcriptional activity of thyroid transcription factor-1 by binding to its homeodomain". J. Biol. Chem. (UNITED STATES) 274 (8): 4640–5. ISSN 0021-9258. PMID 9988700.  

Further reading

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