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Modification of added sugar residue.
It always start in ER but continues to Golgi bodies.
It start witnremoval of 3 glucose and 1 mannose unit.
Enzyme glucosidase remove it.
Before removal of sugars calnexin and calreticulin (chaperons) bind to incompletely folded protein and retain that in ER. These chaperons form disulphide bond in newly formed protein.The disulphide bond formation provides stability to secretory protein outside where extreme environment is present.
An enzyme protein disulphide isomerase also help in disulphide bond formation.
Also lumen of ER has oxidising environment which favors disulphide bond formation.
When 3rd glucose is removed the chaperons are also removed and the protein is folded and transported to Golgi.
Removal of improper protein
Proper confirmation and sugar residues are monitored by UGGT(UDP glucose glycoprotein glucotransferase).
UGGT will interact with folded protein.
If UGGT find improper protein it adds back a glucose molecule, this brings the chaperons calnexin and calreticulin to bind and break the disulphide bond and the reaction is repeated till proper protein is formed.
Another mechanism to get rid of misfolded protein
When protein gets misfolded the hydrophobic regions are exposed.
Due to hydrophobic interaction these protein aggregate and cause other properly folded protein to disrupt their structure and interact with these aggregates.
These misfolded protein themselve act as catalyst.
So, these misfolded proteins are transported to cytoplasm and ubiquitinised by proteosome.
Cystic fibrosis, Alzeimer's disease are examples of misfolded proteins.
It always start in ER but continues to Golgi bodies.
It start witnremoval of 3 glucose and 1 mannose unit.
Enzyme glucosidase remove it.
Before removal of sugars calnexin and calreticulin (chaperons) bind to incompletely folded protein and retain that in ER. These chaperons form disulphide bond in newly formed protein.The disulphide bond formation provides stability to secretory protein outside where extreme environment is present.
An enzyme protein disulphide isomerase also help in disulphide bond formation.
Also lumen of ER has oxidising environment which favors disulphide bond formation.
When 3rd glucose is removed the chaperons are also removed and the protein is folded and transported to Golgi.
Removal of improper protein
Proper confirmation and sugar residues are monitored by UGGT(UDP glucose glycoprotein glucotransferase).
UGGT will interact with folded protein.
If UGGT find improper protein it adds back a glucose molecule, this brings the chaperons calnexin and calreticulin to bind and break the disulphide bond and the reaction is repeated till proper protein is formed.
Another mechanism to get rid of misfolded protein
When protein gets misfolded the hydrophobic regions are exposed.
Due to hydrophobic interaction these protein aggregate and cause other properly folded protein to disrupt their structure and interact with these aggregates.
These misfolded protein themselve act as catalyst.
So, these misfolded proteins are transported to cytoplasm and ubiquitinised by proteosome.
Cystic fibrosis, Alzeimer's disease are examples of misfolded proteins.
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