Question The figure below shows the orientation of a multipass transmembrane pro

Question

Question The figure below shows the orientation of a multipass transmembrane protein after it has completed its entry into the ER membrane (part A) and after it gets delivered to the plasma membrane (part B). This protein has an N-terminal signal sequence (depicted as the dark gray membrane-spanning box), which signal peptidase cleaves off in the endoplasmic reticulum. The other membrane-spanning domains in the protein are represented as open boxes. Given that any hydrophobic membrane-spanning domain can act as either a start-transfer region or a stop-transfer region, draw the final consequences of the actions described below on the orientation of the protein in the plasma membrane. Indicate on your drawing the extracellular space, the cytosolic face, and the plasma membrane, as well as the N- and C-termini of the protein.

A. [4pts] Deleting the first signal sequence

B. [4pts] Changing the hydrophobic amino acids in the first, cleaved, sequence to charged amino acids

C. [4pts] Changing the hydrophobic residues in every other transmembrane sequence to charged residues, starting with the first, cleaved, signal sequence

Explanation / Answer

A. Deleting the first signal sequence ;

Deleting the first signal sequence results in , it cannot be recognised by the ER as it has the signal recognition particle when it binds to ribosomes it is transfering with N terminal ER signal sequence ,so if SRP is removed it is not able to transfered to ER .

B. changing the hydrophobic region amino acids are first cleaved ,sequence to charged amino acids .

if we removed , the start transfer signal sequence is removed , the protein will not be able to transfer the protein . it is located internally and binds to SRP .

c.Changing the hydrophobic residues in every other transmembrane sequence to charged residues, starting with the first, cleaved, signal sequence

protein translocation will not happen at all . as it cannot be recognised and charged aminoacids makes it polar so they cannot be transfferd through the ,memberane

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