TY - JOUR
T1 - Aglycosylated and phosphatidylinositol-anchored MHC class 1 molecules are associated with calnexin
T2 - Evidence implicating the class i-connecting peptide segment in calnexin association
AU - Carreno, Beatriz M.
AU - Schreiber, Kathy L.
AU - McKean, David J.
AU - Stroynowski, Iwona
AU - Hansen, Ted H.
PY - 1995
Y1 - 1995
N2 - The endoplasmic reticulum resident protein calnexin interacts with several glycoproteins including class I MHC molecules. Calnexin is thought to retain free class I heavy chains and/or promote their folding and assembly with β2-microglobulin and peptide ligand. Whereas with other glycoproteins, Asn-linked glycans seem to be involved in calnexin association, with class I molecules the transmembrane region has been implicated. To critically define the structures on class I molecules that determine their interaction with calnexin, we have studied carbohydrate-deficient and transmembrane-variant class I molecules. Carbohydrate-deficient class I molecules were found to accumulate intracellularly in an open, non-β2-microglobulin-associated conformation. However, open as well as conformed class I molecules showed significant calnexin association whether they were aglycosylated or fully glycosylated. Thus, carbohydrate moieties may be necessary for efficient class I folding, but are not required for calnexin association. Calnexin was also found associated with a soluble class I molecule that has a truncated transmembrane segment, demonstrating that membrane attachment of class I is not required for interaction with calnexin. Finally, two isoforms of the class Ib molecule Q7b were compared. Unexpectedly, the glycosylphosphatidylinositol-anchored Q7b isoform was found associated with calnexin, whereas the soluble Q7b isoform was not calnexin associated. These comparisons of Q7b isoforms implicate the class I-connecting peptide segment and not the transmembrane region as a site of interaction with calnexin.
AB - The endoplasmic reticulum resident protein calnexin interacts with several glycoproteins including class I MHC molecules. Calnexin is thought to retain free class I heavy chains and/or promote their folding and assembly with β2-microglobulin and peptide ligand. Whereas with other glycoproteins, Asn-linked glycans seem to be involved in calnexin association, with class I molecules the transmembrane region has been implicated. To critically define the structures on class I molecules that determine their interaction with calnexin, we have studied carbohydrate-deficient and transmembrane-variant class I molecules. Carbohydrate-deficient class I molecules were found to accumulate intracellularly in an open, non-β2-microglobulin-associated conformation. However, open as well as conformed class I molecules showed significant calnexin association whether they were aglycosylated or fully glycosylated. Thus, carbohydrate moieties may be necessary for efficient class I folding, but are not required for calnexin association. Calnexin was also found associated with a soluble class I molecule that has a truncated transmembrane segment, demonstrating that membrane attachment of class I is not required for interaction with calnexin. Finally, two isoforms of the class Ib molecule Q7b were compared. Unexpectedly, the glycosylphosphatidylinositol-anchored Q7b isoform was found associated with calnexin, whereas the soluble Q7b isoform was not calnexin associated. These comparisons of Q7b isoforms implicate the class I-connecting peptide segment and not the transmembrane region as a site of interaction with calnexin.
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M3 - Article
C2 - 7730623
AN - SCOPUS:0029073719
SN - 0022-1767
VL - 154
SP - 5173
EP - 5180
JO - Journal of Immunology
JF - Journal of Immunology
IS - 10
ER -