A research team needs an antibody that binds to a protein of interest so that protein expression can be monitored. They use epitope tagging, adding an epitope (a sequence of amino acids) to the protein through DNA recombination. In this way, they do not need to develop an antibody to the protein, but can use a known, commercially available epitope-specific antibody. However, after following procedure, they are unable to localize the protein. What is a possible reason?

A. The antibody is removed during RNA processing.

B. The commercial antibodies the team used were developed from rat tissues.

C. The added epitope disrupts the function of the tagged protein.

D. The antigen-binding site does not recognize the antibody.

C. The added epitope disrupts the function of the tagged protein

Explanation:

When an additional sequence is tagged to a protein to use comercial antibodies, there are several reasons why this procedure wouldn't work as expected (note that we're assuming the protein is being expressed but it's not possible to detect it).

For example, the sequence of nucleotide added to codify for the tagged epitope are removed during the RNA processing. In that case, the protein would be expressed without the epitope, so it would be impossible to localize it with the antibodies.

Also, it could be that the new epitope is affecting some way the protein folding, making it not functional. This way, it would be degraded by the cell so it wouldn't be detected.

Another possibility is that the epitope doesn't affects the protein folding nor its function, but during the folding ends up in a conformation that makes it inaccesible for the antibody.

In summary, the way as the possible answers to this question are shown, the correct option seems to be C: The added epitope disrupts the function of the target protein.