Question

Antibodies are proteins that are secreted out of the cell. If an NLS was genetically engineered to the C-terminus of an antibody, where do you expect to find it?

a. Outside the cell

b. ER

c. Cytoplasm

d. Nucleus

e. Another organelle

Can you please explain the question too. Thanks

Answer 1

The correct option is d (Nucleus)

Explanation of question- Normally the antibodies are secreted outside the cell usually. For secretion the protein (antibody) travels from endoplasmic reticulum to golgi body then secretory vesicles are formed which fuse to plasma membrane and release the protein (antibody here).

The question asks that what will happen when the c terminal of antibody will be attached by NLS (nuclear localization signal).

Answer- Nuclear localization signal (NLS) is generally rich in basic amino acids. When NLS is present in any protein then it interacts with different class of importins and Ran proteins. Importins and Ran proteins help in entry of protein through nuclear pore complexes and the protein gets inside the nucleus. Therefore, when NLS will be added on  the C terminal of antibody then it will not follow it's usual transport route (secretory) and get secreted out from the cell. But it will go inside the nucleus.

Option a is incorrect as antibody will not be secreted out from the cell but rather get deposited in nucleus

Option b, c and e are also incorrect because the antibody contains nuclear localization signal so, it will not be found in endoplasmic reticulum, cytosol or in any other cell organelle. It will go only inside the nucleus.