Question

What does the conformation-sensing enzyme GT do if it binds to a misfolded or incompletely folded glycoprotein?

1) It degrades the oligosaccharide chain
2) It adds a single mannose back to one of the glucose resides at the exposed end of the recently trimmed oligosaccharide
3) It adds a single glucose back to one of the mannose resides at the exposed end of the recently trimmed oligosaccharide
4) It degrades the protein
5) It refolds the protein on its own

Answer 1

The GT enzyme assists in the folding of glycoproteins by adding a single glucose molecule to an exposed mannose residue on a misfolded or incompletely folded glycoprotein.

Step-by-step explanation:

The conformation-sensing enzyme GT, when it binds to a misfolded or incompletely folded glycoprotein, performs a specific function to facilitate proper folding or degradation. If a glycoprotein is not correctly folded, GT specifically adds a single glucose back to one of the mannose residues at the exposed end of the recently trimmed oligosaccharide. This action is part of a quality control mechanism called the calnexin/calreticulin cycle which ensures that only properly folded glycoproteins are transported out of the endoplasmic reticulum (ER) for further processing in the Golgi apparatus and eventual migration to their functional destinations.