Oligosaccharide modification in the early secretory pathway directs the selection of a misfolded glycoprotein for degradation by the proteasome

被引:209
作者
Liu, Y
Choudhury, P
Cabral, CM
Sifers, RN
机构
[1] Baylor Coll Med, Dept Pathol, Houston, TX 77030 USA
[2] Baylor Coll Med, Dept Cell Biol, Houston, TX 77030 USA
[3] Baylor Coll Med, Cell & Mol Biol Program, Houston, TX 77030 USA
关键词
D O I
10.1074/jbc.274.9.5861
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The role of conformation-based quality control in the early secretory pathway is to eliminate misfolded polypeptides and unassembled multimeric protein complexes from the endoplasmic reticulum, ensuring the deployment of only functional molecules to distal sites. The intracellular fate of terminally misfolded human alpha(1)-antitrypsin was examined in hepatoma cells to identify the functional role of asparagine-linked oligosaccharide modification in the selection of glycoproteins for degradation by the cytosolic proteasome. Proteasomal degradation required physical interaction with the molecular chaperone calnexin. Altered sedimentation of intracellular complexes following treatment with the specific proteasome inhibitor lactacystin, and in combination with mannosidase inhibition, revealed that the removal of mannose from attached oligosaccharides abrogates the release of misfolded alpha(1)-antitrypsin from calnexin prior to proteasomal degradation. Intracellular turnover was arrested with kifunensine, implicating the participation of endoplasmic reticulum mannosidase I in the disposal process. Accelerated degradation occurred in a mannosidase-independent manner and was arrested by lactacystin, in response to the posttranslational inhibition of glucosidase II, demonstrating that the attenuated removal of glucose from attached oligosaccharides functions as the underlying rate-limiting step in the proteasome-mediated pathway. A model is proposed in which the removal of mannose from multiple attached oligosaccharides directs calnexin in the selection of misfolded alpha(1)-antitrypsin for degradation by the proteasome.
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页码:5861 / 5867
页数:7
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