membraneiwitten

Membraneiwitten are proteins that are associated with or embedded in biological membranes. They play essential roles in cellular communication, transport, metabolism, and structural integrity. Based on how tightly they interact with the membrane, they are commonly categorized as integral (intrinsic) membrane proteins, peripheral membrane proteins, or proteins anchored to membranes by covalent lipid attachments.

Integral membrane proteins span the lipid bilayer, typically through one or more hydrophobic transmembrane segments. These segments often adopt alpha-helical or beta-barrel structures. Peripheral membrane proteins associate with the membrane surface, often through electrostatic interactions or after binding to integral proteins. Lipid-anchored proteins attach to membrane lipids via covalent linkages. The arrangement of these proteins determines their exposure to the intracellular and extracellular environments and influences signaling and transport functions.

Biosynthesis and localization involve distinct cellular pathways. In eukaryotes, many membrane proteins are synthesized on ribosomes and co-translationally inserted into the endoplasmic reticulum via the Sec translocon, then trafficked to their final membranes. In mitochondria, chloroplasts, and bacteria, specialized import or insertion systems exist. After insertion, post-translational modifications such as glycosylation or lipidation can modify activity, localization, or stability.

Major classes and functions include receptors (for example, G protein-coupled receptors), ion channels, transporters, enzymes, and adhesion molecules. Membraneiwitten are prominent drug targets due to their central roles in signaling, transport, and metabolism. Studying them presents challenges because of their hydrophobic surfaces and instability outside the membrane, often necessitating specialized methods such as detergents, nanodiscs, or cryo-electron microscopy.