Question

What would you expect to happen to a newly synthesized soluble protein if a mutation caused the deletion of the KDEL sequence?
a. The protein would be returned to the ER in COPI-coated vesicles.
b. The protein will be carried forward through the Golgi apparatus.
c. The protein will be trapped in COPII vesicles .
d. The protein will be incorporated into COPI vesicles.
e. The protein will be recognized by KDEL receptors and a retrieval sequence (KDEL sequence) will be added to it.

Answer 1

After synthesis most of the soluble or non-soluble proteins reach to Golgi. Golgi apparatus decides the next destination.

Proteins synthesized for the lumen of endoplasmic reticulum are recognized by the KDEL sequence present at their carboxyl terminal. This is called ER retrival signal. Mutation in this signal does not allow the protein to bind with KDEL receptor present in Golgi. As a result the protein can't return to endoplasmic reticulum and are carried forward through the Golgi apparatus.