proteinsintegral

Integral membrane proteins, often called integral proteins, are proteins that are permanently embedded in biological membranes. They typically interact with the hydrophobic core of the lipid bilayer through one or more hydrophobic transmembrane segments, and cannot be removed without disrupting the membrane structure. They play diverse roles in transport, signaling, metabolism, and cell architecture.

Integral membrane proteins are commonly classified by their topology. Monotopic proteins interact with only one side of the membrane, while polytopic (multipass) proteins traverse the membrane multiple times. In many organisms, alpha-helical transmembrane proteins predominate, with segments of about 20–25 amino acids forming helices that span the bilayer. In other membranes, such as the outer membranes of Gram-negative bacteria and mitochondria, beta-barrel proteins form channels. Glycosylation and extracellular loops are common in eukaryotic membrane proteins, contributing to recognition and signaling.

Functions range from transport and catalysis to signal transduction and structural support. Transmembrane channels and transporters allow selective passage of ions and metabolites. Receptors, including G protein-coupled receptors, detect external signals and trigger intracellular responses. Membrane-bound enzymes and proteases participate in processing biomolecules at the cell surface. Integral proteins also contribute to cell adhesion and the organization of membrane domains, influencing cell shape and polarity.

Structural biology of integral membrane proteins is challenging due to hydrophobic surfaces. They are studied using detergents, lipid nanodiscs, and advanced techniques such as cryo-electron microscopy, X-ray crystallography, and solution NMR. Examples include bacteriorhodopsin, aquaporins, porins, GPCRs, ion channels, and the Na+/K+ ATPase. Their prominence as drug targets reflects their central roles in physiology and disease.