Question

Problem 4.1.3 (tags: #protein targeting, #protein topology, #transfer sequence) a) Make a map showing the location of signal sequences, start transfer sequences and stop transfer sequences in protein A and protein B below that end up inserted in the membrane as shown. Protein A NH, Cytosol NA J B Scoot & Membrane Protein B COOH HAN Ν - FC ER Cisterna b) Make a map for the arrangement of signal sequences, start transfer sequences and stop transfer sequences for a double pass protein with the N terminal end... • In the cytosol • On the extracellular side of the plasma membrane

Answer 1

Answer a)

Cyto sol wih ) CooH aNH, (B ER Cisterna Protein I Ne t on-cleavable internal - Sequence C C start and a Stop signal to sequence is ame) Protein B Internal stop transfer signal e cleavable N-terminal signal sequence (start transfer signal) In Protein A, which is single-pass trausmembrane proteins have their hycloo- N-terminus on the cytosolic face and the C-terminus on the non- cytosolic C in case ER Cisterna) side. Proteins with this orientation have a single non-cleavable internal signal sequence, which acts as both start transfer signal and functioning as a stop transfer sequence ( membrane- anchor sequence)

In Protein B, N-terminal sequence is ER usterna side and C-terminal at cytosalic side. N-terminal is bryllophable Hydrophilic and C-terminal is hydrophobic in nature. In contains internal stop transfer signal (also acts as membrane- anchor sequence) and cleavable N-terminal signal sequence ( functions as start transfer signal), N-terminal signal sequence initiates cotranslational trauslocation of the protein. Once the N-terminus of the growing polypeptide enters the lumen of the ER, the signal sequence is cleaved. Lator stop strausfor signal stops trausfer of the growing polypeptide. Ca This internal sequence moves laterally and become anchored in the lipid bilayer of the membrane. Although translocation is stoped, translation at the ribosome. is continued for c- terminus syntheses and loop - out.

Answer b)

a (6) map for the arrangement of signal sequences, staut transfer sequences and stop stor transfer sequences for a double pass protein No terminal and in the cytosol. ② autosol cook a NH3 cytosol to start transfer sequence Stop transfer sequence ER lumen An internal ER signal sequence acts as a start trausfer signal and intiates the transfer as the c-terminal part of the protein. At some point, after a stop transfer sequence has entered the trauslocator discharge the sequence tato laterally into the membrane. Coor His Faut-transfer sequence ER LUMEN stop traussfer sequence. The most N-terminal region serve as start- trausfor sequence that causes the preceeling N-termined portion of the protein to be passed across the ER membrane, subsequent hydrophobic sequence function in alternation as start transfer and stop transfer sequence. Prosein N 7 | 19 start Stop Start