Membraneintegrated

Membraneintegrated describes molecules that are embedded within or across biological membranes. The most common examples are integral or intrinsic membrane proteins, which include transmembrane proteins spanning the lipid bilayer and monotopic proteins anchored to one leaflet. Peripheral proteins are not considered membrane-integrated in this sense, as they are surface-associated.

Structure and topology: Transmembrane proteins typically contain hydrophobic transmembrane helices or beta-barrels that traverse the membrane, while beta-barrel porins occur in outer membranes. Topologies include single-pass, multi-pass (polytopic), and beta-barrel arrangements. Insertion and folding are guided by the Sec translocon and specialized chaperones; many proteins are co-translationally targeted to membranes, sometimes via signal peptides or lipid attachments.

Functions: Membrane-integrated proteins mediate transport of ions and molecules, transduce signals, and catalyze reactions within the membrane. Examples include ion channels, transporters (facilitated diffusion and active transport), G protein-coupled receptors, and intramembrane proteases. They play roles in energy production, metabolism, and cell communication.

Significance and context: Membrane integration is essential for compartmentalization in cells and organelles. Failures in proper insertion, folding, or trafficking can cause diseases and are common drug targets. Bacterial outer membranes rely on beta-barrel integral proteins for permeability control; eukaryotic membranes host a diverse repertoire of multi-pass receptors and enzymes.

Study and terminology: The term "membraneintegrated" is often used interchangeably with integral membrane proteins, though some may specify "monotopic" or "bitopic" topologies. Structural studies employ cryo-EM, X-ray crystallography, and NMR, alongside topology prediction and computational modeling to understand insertion, orientation, and dynamics.