Question

A monoclonal antibody was heterologously expressed in E. coli and Chinese hamster ovary (CHO) cell line, and the recombinant proteins obtained were purified to homogeneity and were found to be structurally identical. However, the protein expressed in E. coli was not functionally active. The reason could be

• A. The protein needs glycosylation for its function
• B. E. coli introduced phosphorylation which was detrimental for function
• C. CHO cells generally phosphorylate the heterologously expressed protein
• D. There may be an inactivating ubiquitination modification in E. coli

Hint:

• E. coli → No glycosylation
• CHO cells → Proper PTMs
• Many eukaryotic proteins need glycosylation

Answer 1

The Correct Option is A

Concept: Post-translational modifications (PTMs) are essential for proper protein function.
• Eukaryotic cells (CHO): Perform modifications like glycosylation.
• Prokaryotic cells (E. coli): Lack glycosylation machinery.

Step 1: Analyzing the situation.

• Proteins are structurally identical but function differs.
• Suggests missing post-translational modification.

Step 2: Evaluating options.

• Glycosylation: Required for proper folding/function of antibodies → Correct.
• Phosphorylation in E. coli: Rare and not typical → Incorrect.
• CHO phosphorylation: Not the main functional factor here → Incorrect.
• Ubiquitination in E. coli: Absent in prokaryotes → Incorrect.

Step 3: Selecting the correct answer.
Lack of glycosylation in E. coli leads to loss of functional activity.