ERmembranproteinkomplexet

ER membrane proteins are a diverse group of proteins that reside in or associate with the membrane of the endoplasmic reticulum (ER). They participate in a broad set of processes that are essential for protein maturation, lipid synthesis, calcium storage, and organelle biogenesis. Most ER membrane proteins are integral, containing one or more transmembrane helices, anchoring them in the lipid bilayer, while others are peripherally attached to the membrane or localized to the luminal face.

Key functions include: protein import and translocation into the ER lumen or membrane, mediated by translocon complexes such as Sec61; folding and maturation of secretory and membrane proteins, aided by luminal chaperones such as calnexin and calreticulin and by enzymes such as the protein disulfide isomerase family; and co-translational and post-translational modifications, including glycosylation by the oligosaccharyltransferase (OST) complex linked to the membrane. ER membrane proteins also organize lipid biosynthesis and participate in calcium storage and signaling, with pumps like the SERCA Ca2+-ATPases and calcium channels embedded in the ER membrane.

The ER quality control system relies on membrane-anchored sensors and chaperones to detect misfolded proteins and direct them toward degradation via ER-associated degradation (ERAD). In stress conditions, signaling branches of the unfolded protein response (UPR) are initiated by transmembrane sensors such as IRE1, PERK, and ATF6.

Defects in ER membrane proteins are associated with various diseases, including cystic fibrosis caused by misfolded CFTR and disorders linked to disrupted calcium homeostasis. Understanding these proteins is essential for cell biology and biomedical research.