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Structural basis of carbohydrate recognition by calreticulin
Structural highlights
FunctionCALR_MOUSE Calcium-binding chaperone that promotes folding, oligomeric assembly and quality control in the endoplasmic reticulum (ER) via the calreticulin/calnexin cycle. This lectin interacts transiently with almost all of the monoglucosylated glycoproteins that are synthesized in the ER. Interacts with the DNA-binding domain of NR3C1 and mediates its nuclear export. Involved in maternal gene expression regulation. May participate in oocyte maturation via the regulation of calcium homeostasis (By similarity).[1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe calnexin cycle is a process by which glycosylated proteins are subjected to folding cycles in the endoplasmic reticulum lumen via binding to the membrane protein calnexin (CNX) or to its soluble homolog calreticulin (CRT). CNX and CRT specifically recognize monoglucosylated Glc(1)Man(9)GlcNAc(2) glycans, but the structural determinants underlying this specificity are unknown. Here, we report a 1.95-A crystal structure of the CRT lectin domain in complex with the tetrasaccharide alpha-Glc-(1-->3)-alpha-Man-(1-->2)-alpha-Man-(1-->2)-Man. The tetrasaccharide binds to a long channel on CRT formed by a concave beta-sheet. All four sugar moieties are engaged in the protein binding via an extensive network of hydrogen bonds and hydrophobic contacts. The structure explains the requirement for glucose at the nonreducing end of the carbohydrate; the oxygen O(2) of glucose perfectly fits to a pocket formed by CRT side chains while forming direct hydrogen bonds with the carbonyl of Gly(124) and the side chain of Lys(111). The structure also explains a requirement for the Cys(105)-Cys(137) disulfide bond in CRT/CNX for efficient carbohydrate binding. The Cys(105)-Cys(137) disulfide bond is involved in intimate contacts with the third and fourth sugar moieties of the Glc(1)Man(3) tetrasaccharide. Finally, the structure rationalizes previous mutagenesis of CRT and lays a structural groundwork for future studies of the role of CNX/CRT in diverse biological pathways. Structural basis of carbohydrate recognition by calreticulin.,Kozlov G, Pocanschi CL, Rosenauer A, Bastos-Aristizabal S, Gorelik A, Williams DB, Gehring K J Biol Chem. 2010 Dec 3;285(49):38612-20. Epub 2010 Sep 29. PMID:20880849[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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