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Related Concept Videos

Protein Folding Quality Check in the RER01:29

Protein Folding Quality Check in the RER

ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system that folds and assesses the confirmation of N-glycosylated proteins before they can exit the ER lumen. The primary players of this quality check pipeline are the lectins, ER-resident chaperones, and a glucosyl transferase enzyme. In case the calnexin system in the lumen fails to salvage a misfolded protein, it is transported to the cytoplasm...
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The nucleus restricts several proteins within and allows others to pass. The restricted proteins possess a nuclear retention sequence or NRS, anchoring them to the nuclear lamins and preventing their transport to the cytosol. The non-restricted proteins, after their synthesis, are transported to their site of action, such as the cytosol or other organelles, with the help of nuclear export signals or NES.
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Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates
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Substrate-specific requirements for UGT1-dependent release from calnexin.

Tatiana Soldà1, Carmela Galli1, Randal J Kaufman2

  • 1Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland.

Molecular Cell
|July 24, 2007
PubMed
Summary

The UDP-glucose:glycoprotein glucosyltransferase (UGT1) enzyme plays a dual role in glycoprotein folding within the endoplasmic reticulum. While typically promoting prolonged calnexin binding, UGT1 deletion unexpectedly delays release for some proteins, suggesting a role in ER export.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Protein Folding

Background:

  • Newly synthesized glycoproteins bind to the ER chaperone calnexin for folding, aided by ERp57.
  • The UDP-glucose:glycoprotein glucosyltransferase (UGT1) re-glucosylates misfolded glycoproteins, retaining them in the calnexin system.
  • This process facilitates additional folding attempts for nonnative polypeptides.

Purpose of the Study:

  • To investigate the role of UGT1 in glycoprotein folding and release from the calnexin system.
  • To determine how UGT1 deletion affects the folding kinetics of different glycoproteins.

Main Methods:

  • Analysis of glycoprotein binding and release from calnexin in UGT1-deleted cells.
  • Comparison of folding pathways for various newly synthesized glycoproteins.

Main Results:

  • UGT1 deletion had no effect on calnexin binding for some glycoproteins, indicating a single-event folding pathway.
  • For other glycoproteins, UGT1 deletion led to premature release from calnexin, suggesting a role in facilitating multiple folding cycles.
  • Unexpectedly, UGT1 deletion delayed ER export for certain glycoproteins, implying UGT1 is necessary for structural maturation required for dissociation.

Conclusions:

  • UGT1's function is more complex than solely prolonging calnexin retention; it influences glycoprotein release kinetics.
  • UGT1 activity is crucial for the timely dissociation of specific glycoproteins from calnexin and their subsequent ER export.
  • The study reveals a novel role for UGT1 in facilitating structural maturation necessary for efficient protein trafficking from the ER.