Question

Briefly describe the mechanism by which an internal stop-transfer sequence in a protein causes the protein to become embedded in the lipid bilayer as a transmembrane protein with a single membrane-spanning region. Assume that the protein has an N-terminal signal sequence and just one internal hydrophobic stop-transfer sequence

Answer 1

The start signal sequence refers to an internal hydrophobic residue that is dissimilar to the signal sequence present at the N-terminal. It associates with the signal receptor particle that combines with the SRP receptor on the membrane. However, unlike the N-terminal signal sequence it is not cleaved.

The stop-transfer signal is also an internal hydrophobic membrane crossing sequence, which follows the start sequence. As soon the translocation machinery comes in contact with the stop-transfer sequence it gets disassembled, the peptide does not get cleaved, however, the translation takes place spontaneously. In this manner, a single start-stop transfer sequence anchors the protein.