A CLEAVABLE N-TERMINAL SIGNAL PEPTIDE IS NOT A PREREQUISITE FOR THE BIOSYNTHESIS OF GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED PROTEINS

During the biosynthesis of glycosylphosphatidylinositol (GPI)-anchored proteins, an N-terminal signal peptide is used to direct biosynthesis to the endoplasmic reticulum. It was previously unknown whether or no t this signal must be removed during the biosynthesis of GPI-anchored proteins. Using neutral endopeptidase (EC 3.4.24.11), a well character ized type II membrane protein that is attached to the membrane via an uncleaved N-terminal signal peptide, we extended its C terminus with 3 3 of the 37 amino acids of the GPI anchor signal sequence of decay-acc elerating factor. When expressed in COS-1 and Chinese hamster fibrobla st (CHW) cells, the protein was shown to possess both transmembrane an d GPI anchors, indicating that a cleavable N-terminal signal peptide i s not a prerequisite for the biosynthesis of GPI-anchored proteins.