Endoplasmic Reticulum

ID #2136

I understand that when there is a transmembrane protein made with its N-terminus on the cytoplasmic side, there is no cleavage of the signal peptide. What about when there is a transmembrane protein made with the N-terminus inside the lumen? Does this signal peptide get cleaved?


You are correct. If a transmembrane protein has its N terminus in the lumen of the ER, it has to display an amino-terminal signal peptide which is cleaved by signal peptidase. Given how the protein is looped into the translocon during translation, the only way for a protein to have its N terminus in the lumen is for the signal peptide to be at the very N-terminus of the protein which will be cleaved off.

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