Transmembranregion

Transmembranregion, more commonly referred to as the transmembrane region or transmembrane domain (TMD), is a hydrophobic segment of a protein that spans a biological membrane. In most proteins, this region is an alpha helix about 20–25 amino acids long, though in some cases especially in outer membrane proteins the spanning segment may adopt a beta-barrel fold. The transmembranregion serves to anchor the protein in the lipid bilayer and largely determines its membrane topology.

Topology and integration are guided by topogenic signals such as signal peptides and stop-transfer anchors, which direct insertion and orientation in the membrane. Proteins can be single-pass, with one transmembranregion, or multi-pass, containing several such regions that create complex membrane architectures.

Functions associated with the transmembranregion include acting as an anchor, forming or contributing to channels and transport pathways, and organizing active sites or interaction surfaces at the membrane. Examples include G protein-coupled receptors, which typically have seven transmembrane helices, and various ion channels and enzymes that rely on membrane-spanning segments for activity and regulation.

Prediction and study of transmembranregions are central in bioinformatics and structural biology. Hydrophobicity analyses and specialized algorithms (for example, those used to predict transmembrane helices) are commonly employed, often complemented by experimental validation through biochemical, proteomic, or structural methods.

Notes: while the canonical view emphasizes hydrophobic, membrane-spanning helices, some membrane-associated segments are amphipathic helices lying along the membrane surface, and beta-barrel membranes involve different spanning patterns. Mislocalization or mutations in transmembranregions can impair protein function and trafficking.