Disease relevance of CANX

• Expression using the baculovirus Sf9 insect cell system of a recombinant truncated calnexin corresponding to residues 1-462 (calnexin delta TMC) revealed an association in vivo with a coexpressed secretory glycoprotein substrate, human immunodeficiency virus type I gp120 [1].

High impact information on CANX

• Glucose trimming and reglucosylation determine glycoprotein association with calnexin in the endoplasmic reticulum [2].
• Release of fully folded HA from calnexin required the removal of the remaining glucose by glucosidase II [2].
• These steps include cleavage of the signal sequence, glycosylation, binding by the chaperones calnexin and calreticulin, and the oxidoreductase ERp57, and oxidation [3].
• Analysis by two-dimensional phosphopeptide maps revealed that calnexin was in vitro phosphorylated in isolated microsomes by casein kinase 2 (CK2) and extracellular-signal regulated kinase-1 (ERK-1) at sites corresponding to those for in vivo phosphorylation [4].
• Although the role of the ER luminal domain of calnexin has been established as a constituent of the molecular chaperone machinery of the ER, less is known about the role of the cytosolic phosphorylation of calnexin [4].

Biological context of CANX

• The open reading frame encodes a polypeptide with 530 amino acids, a molecular mass of 60.5 kDa, and overall 48% identity to dog calnexin [5].
• The deduced amino acid sequence has 58% homology with dog calnexin (the ER membrane phosphoprotein of pancreatic cells) and significant partial homology with calreticulin (high affinity Ca(2+)-binding protein of the ER membrane) at the repetitive sequence [6].
• In this study we report the computer analysis of the predicted amino acid sequence of this calnexin-like melanosomal protein [7].

Anatomical context of CANX

• Calnexin and ERp57 act cooperatively to ensure a proper folding of proteins in the endoplasmic reticulum (ER) [8].
• Protease protection experiments with intact canine rough microsomes showed that amino acid residues 1-462 of calnexin are located within the lumen of the endoplasmic reticulum [1].
• To determine their role in the maturation of newly synthesized glycoproteins, we analyzed the folding and trimerization of in vitro translated influenza hemagglutinin (HA) in canine pancreas microsomes under conditions in which HA's interactions with CNX and CRT could be manipulated [9].
• Calnexin fails to associate with substrate proteins in glucosidase-deficient cell lines [10].
• Here we describe that the lumenal surface of the ER membranes transiently tethers the folding intermediate of secretory proteins via a 90-kDa ER membrane protein, calnexin [11].

Associations of CANX with chemical compounds

• Our results identify the luminal domain of calnexin as responsible for binding substrates, Ca2+, and Mg-ATP [1].
• Triton X-114 partitioning of the integral membrane proteins of rough microsomes suggested that pgp35 (SSR alpha) and calnexin were major Ca(2+)-binding proteins of the endoplasmic reticulum membrane [12].
• We demonstrate that the properties of the purified calnexin delta TMC correspond to those of full-length calnexin in canine microsomes with at least one intramolecular disulfide bond and binding to 45Ca2+ [1].
• If HA's binding to CNX and CRT was inhibited using a glucosidase inhibitor, castanospermine (CST), the rate of disulfide formation and oligomerization was doubled but the overall efficiency of maturation of HA decreased due to aggregation and degradation [9].
• Perturbation of the redox state by 5 mM dithiothreitol or 1 mM diamide markedly inhibited the dissociation of p70 from calnexin (t1/2 > 30 min) [11].

Analytical, diagnostic and therapeutic context of CANX

• In vivo, calnexin-associated ERK-1 activity was identified by co-immunoprecipitation [4].
• Using ryanodine-mediated calcium oxalate loading of SR vesicles followed by density gradient centrifugation, we have shown that calnexin is a bona fide SR protein and an integral constituent of both junctional and free SR vesicles [13].
• Immunofluorescence due to intracellular alpha2CAR partially overlaps that due to calnexin, a marker for endoplasmic reticulum, as well as that due to mannosidase II, a marker for the trans-Golgi network [14].
• Identification and crystallization of a protease-resistant core of calnexin that retains biological activity [15].
• Furthermore, we demonstrated that TCR-alpha coprecipitated with calnexin migrated between unglucosylated and diglucosylated forms on SDS-PAGE [16].

References