Transmembrana

Transmembrana is a term used to describe anything that spans a biological membrane. In biology, transmembrane elements include regions of proteins or other macromolecules that extend from one side of a membrane to the other, crossing the hydrophobic core of the lipid bilayer.

Transmembrane proteins are a major class of integral membrane proteins. They typically contain one or more transmembrane segments composed of hydrophobic amino acids that form alpha helices or, in some cases, beta barrels. Most single-pass proteins cross the membrane once; multi-pass proteins traverse it several times, creating complex topologies and functional motifs such as channels and receptors.

Protein insertion and orientation are coordinated during synthesis. Most transmembrane segments are embedded in the endoplasmic reticulum membrane during translation via the Sec translocon. Signal peptides guide initial insertion, and the positive-inside rule helps determine the cytoplasmic versus extracellular orientation. Beta-barrel transmembrane proteins occur mainly in the outer membranes of Gram-negative bacteria and in mitochondrial and chloroplast outer membranes, assisted by dedicated assembly machineries.

Functions of transmembrane proteins include transport of ions and molecules, signal transduction, enzymatic activity, and cell adhesion. Examples include aquaporin water channels, ion channels, transporters, and G protein-coupled receptors. The transmembrane region is often the site of pharmacological targeting, because it participates directly in gating, transport, or signaling.

Advances in structural biology, such as X-ray crystallography, cryo-electron microscopy, and computational topology analyses, have expanded understanding of transmembrane architecture and dynamics. Malfunction or misfolding of transmembrane domains is associated with diseases, including channelopathies and neurodegenerative conditions.