Protein X contains four transmembrane domains, a short N-terminus and a long C-terminus. Following protein synthesis, the N-terminus of the protein faces the lumen (the inside) of the endoplasmic reticulum. After protein X is transported to the cell surface via exocytosis, you would expect the C-terminus of the protein X to be Multiple choice question. A) extracellular. B) cytoplasmic. C) in the lumen. D) in the lipid bilayer of the plasma membrane.