GPI-anchored proteins are synthesized
A) on free ribosomes and attached to the GPI group on the outside of the ER.
B) as transmembrane proteins, then are cleaved and joined to the GPI group on the cytosolic surface of the ER.
C) as transmembrane proteins, then are cleaved and joined to the GPI group on the lumenal surface of the ER.
D) on free ribosomes and attached to the GPI group on the cytosolic surface of the ER.

Question

Quizplus · Accepted Answer

GPI-anchored proteins are initially synthesized as transmembrane proteins, with a C-terminal signal peptide recognized by the ER signal recognition particle (SRP) that gets inserted into the ER membrane. Once inside the ER, the signal peptide is cleaved off and the protein is modified by the addition of a GPI (glycosylphosphatidylinositol) anchor to the C-terminus. The GPI anchor is added on the lumenal (or luminal) side of the ER membrane and the released peptide is then noncovalently bound to the outer leaflet of the plasma membrane.

GPI-Anchored Proteins Are Synthesized