Endoplasmic Reticulum Marker

The endoplasmic reticulum is a membrane-bound organelle that is critical to the proper sorting and folding of proteins. Improperly folded proteins are normally allowed to refold into their functional conformation, and if not possible to repair, these unfolded proteins are directed to be degraded to prevent damage to the cell. The P4HB gene encodes a protein disulfide isomerase (PDI) that catalyzes both the formation of disulfide bonds, which form between cysteine residues to stabilize protein structure, and isomerization between or within molecules of secreted proteins. To achieve the natural conformation, this process takes place in the endoplasmic reticulum, so P4HB is often used as an ER marker. Studies on the oxidative folding mechanism indicate that molecular oxygen can oxidize the ER protein Ero1, and Ero1 can oxidize PDI through a disulfide bond. After this activity, PDI catalyzes the folding of proteins to form disulfide bonds.