You are studying the calnexin protein, To study the calnexin protein more, you d

Question

You are studying the calnexin protein, To study the calnexin protein more, you decide to mutate the amino acids KKRR found on the C-terminal end in calnexin to amino acids AAAA, to see how this might affect it’s function.

A. What is the original function of calnexin, and where does it reside? (2 pts)

B. First you test the function of calnexin in a test tube, and you find that it doesn’t lose it’s original activity. However, cells that contain only the mutated form (AAAA) of calnexin do not function correctly. Please explain (be specific) how the mutation (AAAA) is affecting Calnexin’s role in the cell. (3 pts)

C. Please explain how the mutation (AAAA) might affect other proteins that enter into the endomembrane system. (3 pts)

Explanation / Answer

Answer:

A. Function of calnexin are 1. molecular chaperones to assist in the folding of glycoproteins, MHC I

2. also participate in quality control by prolonged interaction with misfolded or incompletely assembled proteins.

It resides as integral membrane protein of the Endoplasmic reticulum.

B.  The mutation (AAAA) is affecting Calnexin’s role in the cell as this mutation is on C-terminal side andcterminal become neutral as in non mutated it was a sequence of polar amino acids. The c-terminal cytosolic domain was hydroplilic ,highly charged that binds Ca2+ with moderate affinity. so after mutation its affinity towards Ca2+ will reduce and affect its role.

C. The mutation (AAAA) might affect other proteins that enter into the endomembrane system by altering protien folding or modification.

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