Purification and characterization of a soluble calnexin from human placenta.
Calreticulin (Crt) and calnexin (Cnx) are homologous endoplasmic reticulum (ER) chaperones involved in protein folding and quality control. Crt is a soluble ER luminal Mr 46 kDa protein and Cnx is a Mr 67kDa ER membrane protein. During purification of Crt from human placenta a soluble form of Cnx (sCnx) was consistently identified in a separate ion exchange chromatography peak. The sCnx was further purified and characterised. This showed that the protein had been cleaved after residue 472 (between Gln and Met), thus liberating it from the transmembrane and cytoplasmic parts of Cnx. The extraction and initial purification steps were carried out in the presence of protease inhibitors, thus ruling out that the cleavage was an artefact of the isolation procedure. This indicates that sCnx may have a physiological chaperone function similar to that of Crt.
Department of Clinical Biochemistry, Immunology and Genetics, Statens Serum Institut, Artillerivej 5, DK-2300 Copenhagen, Denmark.
Dorthe T
DT
Olsen
Li
L
Peng
Sofie D
SD
Træholt
Karen
K
Duus
Peter
P
Højrup
Gunnar
G
Houen
D037281:Calnexin / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D037282:Calreticulin / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006801:Humans; D010920:Placenta / Q000737:chemistry* / Q000378:metabolism; D011247:Pregnancy; D012995:Solubility
D037282:Calreticulin; D037281:Calnexin
Calnexin; Calreticulin; Chaperone; Placenta; Purification; Soluble