Calnexin 2912509 224262611 2008-07-08T01:36:01Z ProteinBoxBot 3991663 Replaced protein Box Template with PBB Template for easy viewing. {{PBB|geneid=821}} '''Calnexin (CNX)''' is a 90kDa [[integral protein]] of the [[endoplasmic reticulum]] (ER). It consists of a large (50 kDa) [[N-terminal]] [[calcium]]-[[Binding (molecular)|binding]] [[Lumen (anatomy)|lumenal]] [[protein domain|domain]], a single [[transmembrane helix]] and a short (90 [[Residue (chemistry)|residues]]), [[acid]]ic [[cytoplasm]]ic tail. Calnexin is one of the [[Chaperone (protein)|chaperone]] molecules, which are characterized by their main function of assisting [[protein folding]] and quality control, ensuring that only properly folded and assembled proteins proceed further along the [[secretory pathway]]. The function of calnexin is to retain unfolded or unassembled N-linked [[glycoproteins]] in the endoplasmic reticulum. Calnexin binds only those N-[[glycoprotein]]s that have GlcNAc2Man9Glc1 [[oligosaccharide]]s. Oligosaccharides with three sequential [[glucose]] residues are added to [[asparagine]] residues of the nascent proteins in the ER. The monoglucosylated oligosaccharides that are recognized by calnexin result from the trimming of two glucose residues by the sequential action of two [[glucosidase]]s, I and II. Glucosidase II can also remove the third and last glucose residue. If the glycoprotein is not properly folded, an enzyme called [[UGGT]] (for UDP-glucose:glycoprotein glucosyltransferase) will add the glucose residue back onto the oligosaccharide thus regenerating the glycoprotein's ability to bind to calnexin. The improperly-folded glycoprotein chain thus loiters in the ER, risking the encounter with MNS1 ([[alpha-mannosidase]]), which eventually sentences the underperforming glycoprotein to [[Chemical decomposition|degradation]] by removing its [[mannose]] residue. [[Adenosine triphosphate|ATP]] and [[Ca++]] are two of the cofactors involved in substrate binding for calnexin. Calnexin also functions as a chaperone for the folding of [[MHC class I]] alpha chain in the membrane of the ER. After folding is completed Calnexin is replaced by [[Calreticulin]], which assists in further assembly of MHC class I. ==External links== * {{MeshName|Calnexin}} ==Further reading== {{refbegin | 2}} {{PBB_Further_reading | citations = *{{cite journal | author=Kleizen B, Braakman I |title=Protein folding and quality control in the endoplasmic reticulum. |journal=Curr. Opin. Cell Biol. |volume=16 |issue= 4 |pages= 343–9 |year= 2005 |pmid= 15261665 |doi= 10.1016/j.ceb.2004.06.012 }} *{{cite journal | author=Rasmussen HH, van Damme J, Puype M, ''et al.'' |title=Microsequences of 145 proteins recorded in the two-dimensional gel protein database of normal human epidermal keratinocytes. |journal=Electrophoresis |volume=13 |issue= 12 |pages= 960–9 |year= 1993 |pmid= 1286667 |doi= }} *{{cite journal | author=Galvin K, Krishna S, Ponchel F, ''et al.'' |title=The major histocompatibility complex class I antigen-binding protein p88 is the product of the calnexin gene. |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=89 |issue= 18 |pages= 8452–6 |year= 1992 |pmid= 1326756 |doi= }} *{{cite journal | author=Pind S, Riordan JR, Williams DB |title=Participation of the endoplasmic reticulum chaperone calnexin (p88, IP90) in the biogenesis of the cystic fibrosis transmembrane conductance regulator. |journal=J. Biol. Chem. |volume=269 |issue= 17 |pages= 12784–8 |year= 1994 |pmid= 7513695 |doi= }} *{{cite journal | author=Honoré B, Rasmussen HH, Celis A, ''et al.'' |title=The molecular chaperones HSP28, GRP78, endoplasmin, and calnexin exhibit strikingly different levels in quiescent keratinocytes as compared to their proliferating normal and transformed counterparts: cDNA cloning and expression of calnexin. |journal=Electrophoresis |volume=15 |issue= 3-4 |pages= 482–90 |year= 1994 |pmid= 8055875 |doi= }} *{{cite journal | author=Tjoelker LW, Seyfried CE, Eddy RL, ''et al.'' |title=Human, mouse, and rat calnexin cDNA cloning: identification of potential calcium binding motifs and gene localization to human chromosome 5. |journal=Biochemistry |volume=33 |issue= 11 |pages= 3229–36 |year= 1994 |pmid= 8136357 |doi= }} *{{cite journal | author=Lenter M, Vestweber D |title=The integrin chains beta 1 and alpha 6 associate with the chaperone calnexin prior to integrin assembly. |journal=J. Biol. Chem. |volume=269 |issue= 16 |pages= 12263–8 |year= 1994 |pmid= 8163531 |doi= }} *{{cite journal | author=Rajagopalan S, Xu Y, Brenner MB |title=Retention of unassembled components of integral membrane proteins by calnexin. |journal=Science |volume=263 |issue= 5145 |pages= 387–90 |year= 1994 |pmid= 8278814 |doi= }} *{{cite journal | author=David V, Hochstenbach F, Rajagopalan S, Brenner MB |title=Interaction with newly synthesized and retained proteins in the endoplasmic reticulum suggests a chaperone function for human integral membrane protein IP90 (calnexin). |journal=J. Biol. Chem. |volume=268 |issue= 13 |pages= 9585–92 |year= 1993 |pmid= 8486646 |doi= }} *{{cite journal | author=Bellovino D, Morimoto T, Tosetti F, Gaetani S |title=Retinol binding protein and transthyretin are secreted as a complex formed in the endoplasmic reticulum in HepG2 human hepatocarcinoma cells. |journal=Exp. Cell Res. |volume=222 |issue= 1 |pages= 77–83 |year= 1996 |pmid= 8549676 |doi= 10.1006/excr.1996.0010 }} *{{cite journal | author=Otteken A, Moss B |title=Calreticulin interacts with newly synthesized human immunodeficiency virus type 1 envelope glycoprotein, suggesting a chaperone function similar to that of calnexin. |journal=J. Biol. Chem. |volume=271 |issue= 1 |pages= 97–103 |year= 1996 |pmid= 8550632 |doi= }} *{{cite journal | author=Devergne O, Hummel M, Koeppen H, ''et al.'' |title=A novel interleukin-12 p40-related protein induced by latent Epstein-Barr virus infection in B lymphocytes. |journal=J. Virol. |volume=70 |issue= 2 |pages= 1143–53 |year= 1996 |pmid= 8551575 |doi= }} *{{cite journal | author=Andersson B, Wentland MA, Ricafrente JY, ''et al.'' |title=A "double adaptor" method for improved shotgun library construction. |journal=Anal. Biochem. |volume=236 |issue= 1 |pages= 107–13 |year= 1996 |pmid= 8619474 |doi= 10.1006/abio.1996.0138 }} *{{cite journal | author=van Leeuwen JE, Kearse KP |title=Calnexin associates exclusively with individual CD3 delta and T cell antigen receptor (TCR) alpha proteins containing incompletely trimmed glycans that are not assembled into multisubunit TCR complexes. |journal=J. Biol. Chem. |volume=271 |issue= 16 |pages= 9660–5 |year= 1996 |pmid= 8621641 |doi= }} *{{cite journal | author=Oliver JD, Hresko RC, Mueckler M, High S |title=The glut 1 glucose transporter interacts with calnexin and calreticulin. |journal=J. Biol. Chem. |volume=271 |issue= 23 |pages= 13691–6 |year= 1996 |pmid= 8662691 |doi= }} *{{cite journal | author=Li Y, Bergeron JJ, Luo L, ''et al.'' |title=Effects of inefficient cleavage of the signal sequence of HIV-1 gp 120 on its association with calnexin, folding, and intracellular transport. |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=93 |issue= 18 |pages= 9606–11 |year= 1996 |pmid= 8790377 |doi= }} *{{cite journal | author=Trombetta ES, Simons JF, Helenius A |title=Endoplasmic reticulum glucosidase II is composed of a catalytic subunit, conserved from yeast to mammals, and a tightly bound noncatalytic HDEL-containing subunit. |journal=J. Biol. Chem. |volume=271 |issue= 44 |pages= 27509–16 |year= 1996 |pmid= 8910335 |doi= }} *{{cite journal | author=Tatu U, Helenius A |title=Interactions between newly synthesized glycoproteins, calnexin and a network of resident chaperones in the endoplasmic reticulum. |journal=J. Cell Biol. |volume=136 |issue= 3 |pages= 555–65 |year= 1997 |pmid= 9024687 |doi= }} *{{cite journal | author=Wiest DL, Bhandoola A, Punt J, ''et al.'' |title=Incomplete endoplasmic reticulum (ER) retention in immature thymocytes as revealed by surface expression of "ER-resident" molecular chaperones. |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=94 |issue= 5 |pages= 1884–9 |year= 1997 |pmid= 9050874 |doi= }} *{{cite journal | author=Yu W, Andersson B, Worley KC, ''et al.'' |title=Large-scale concatenation cDNA sequencing. |journal=Genome Res. |volume=7 |issue= 4 |pages= 353–8 |year= 1997 |pmid= 9110174 |doi= }} }} {{refend}} {{Calcium-binding proteins}} {{Lectins}} {{Membrane proteins}} {{protein-stub}} [[Category:Integral membrane proteins]] [[de:Calnexin]] <!-- The PBB_Controls template provides controls for Protein Box Bot, please see Template:PBB_Controls for details. --> {{PBB_Controls | update_page = yes | require_manual_inspection = no | update_protein_box = yes | update_summary = no | update_citations = yes }}