BIOB10H3 Lecture Notes - Lecture 6: Calreticulin, Protein Folding, Calnexin
Document Summary
Proteins in the er have oligosaccharides that are added to them. Oligosaccharides: a string of monosaccharides: cannot be hydrolyzed. Protein glycosylation: the process of adding the oligosaccharide to a protein: catalyzed by oligosacchardyl transferase (i. e. glycosyl transferase) The oligosaccharide is added to the amino group of an asparagine (an aa) The protein is referred to as n-linked or asparagine-linked. Oligosaccharide addition plays a role in protein quality control. Er chaperone proteins: calnexin, calreticulin, both are lectins (b/c they bind to carbohydrates) Er chaperone proteins function as folding police to prevent misfolded proteins from leaving the er: they can only function if they are bound to oligosaccharide. Glucose is removed by glucosidase one at a time until one remains. Calnexin or calreticulin binds to the last glucose. Glucosidase removes the last glucose and release the protein from calnexin or calreticulin: the protein now has n-linked oligosaccharide but no glucoses. Glucosyl transferase determines if the protein is folded properly.
