Chinese Academy of Sciences Apr 2 2025 The endoplasmic reticulum (ER) is the portion of the cell responsible for manufacturing and folding proteins. Proteins are essential for a wide range of cellular functions-as enzymes, transporters, hormones, antibodies, receptors, and more. They must be folded into the correct three-dimensional shape to function properly. If the ER is unable to manufacture or fold proteins correctly, the cell develops ER stress, which activates the unfolded protein