Calreticulin
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Date: 2021-12-10

Calreticulin, by Wikipedia https://en.wikipedia.org/wiki?curid=7120 / CC BY SA 3.0

#Genes_on_human_chromosome_19
#C-type_lectins
#Immune_system
#Transcription_coregulators
#Molecular_chaperones
Calreticulin also known as calregulin, CRP55, CaBP3, calsequestrin-like protein, and endoplasmic reticulum resident protein 60 （ERp60） is a protein that in humans is encoded by the CALR gene.
Calreticulin is a multifunctional soluble protein that binds Ca2+ ions （a second messenger 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 trisphosphate）.
Calreticulin is located in storage compartments associated with the endoplasmic reticulum and is considered an ER resident protein.
The term "Mobilferrin" is considered to be the same as calreticulin by some sources.
Calreticulin binds to misfolded proteins and prevents them from being exported from the endoplasmic reticulum to the Golgi apparatus.
A similar quality-control molecular chaperone, calnexin, performs the same service for soluble proteins as does calreticulin, however it is a membrane-bound protein.
Both proteins, calnexin and calreticulin, have the function of binding to oligosaccharides containing terminal glucose residues, thereby targeting them for degradation.
Calreticulin and Calnexin's ability to bind carbohydrates associates them with the lectin protein family.
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.
Studies on transgenic mice reveal that calreticulin is a cardiac embryonic gene that is es...