Signal peptidase

Signal peptidases are enzymes that convert secretory and some membrane proteins to their mature forms by cleaving their signal peptides from their N-terminals.

Signal peptidases were initially observed in endoplasmic reticulum (ER)-derived membrane fractions isolated from mouse myeloma cells. The key observation by César Milstein and colleagues was that immunoglobulin light chains were produced in a higher molecular weight form, which became processed by the ER membrane fraction. This finding was directly followed by the discovery of the translocation machinery. Signal peptidases are also found in prokaryotes as well as the protein import machinery of mitochondria and chloroplasts.