Question

Beside the SRP path, are there other options for getting a protein into the ER? What are they and explain their mechanism of entry?

Describe the structure of the translocon sec61 and its partners. how is it plugged and how does the seam allow lateral transfer

Answer 1

Apart from the SRP path for the entry of proteins in the ER, another way of the entry is through translocon which is a pore like protein structure that enables movement of the protein through it. One of the prominent one is translocon Sec61 and it helps in transportation of the protein in the endoplasmic reticulum. The translocon consists of a plug which blocks protein movement in and out of the ER and the protein enters through it by displacing the plug. When the polypeptide chain is formed, the hydrophobic region binds to the Sec61 region and hence enables the translocation of the protein within the lumen of the endoplasmic reticulum.

The structure of the translocon sec61 consists of two transmembrane halves spanning through segments 1 – 5 and from segments 6 to 10. The translocon consists of a channel which is plugged until displaced by the protein. The extracellular funnel comes with a plug and the pore consists of a complex of six hydrophobic amino acid and they have their side chain that projection towards inside. As the protein translocation takes place, it leads to the movement of the plug and hence the protein is able to enter through the pore into the extracellular space.