Question

Utilizing recombinant DNA technology methods, a DNA sequence coding for the KDEL peptide region characteristic of ER resident proteins was engineered into a gene for a protein that is destined to be secreted out of a cell (eg., Insulin protein that is secreted by pancreatic acinar cells). The hybrid secretory protein coding gene bearing the KDEL coding sequence was introduced into cultured pancreatic cells. You would expect:

a.       the hybrid secretory protein would be secreted out of the cell and appear in the culture medium in the petridish.

b.       the hybrid secretory protein would end up in the cell membrane

c.       the hybrid secretory protein would be transported to the lysosome

d.       the hybrid secretory protein would be retrieved through COP1 vesicles back into the ER

e.       none of the above

Answer 1

d. the hybrid secretory protein would be retrieved through COP1 vesicles back into the ER

KDEL sequence is present at the C-terminal of the amino acid sequence in proteins. It serves to retain the proteins in the ER and also to bring back the protein to ER if it is accidentally secreted out of it. Normally, protein is transported from the ER to the cis-golgi via COPII vesicles. However, an engineered KDEL sequence in the protein will lead to retrograde transport of protein back into the ER from Golgi through COP1 vesicles.