translocators

Translocators are molecular machines that move substances across cellular membranes or within subcellular compartments. The term covers a broad set of proteins and complexes that enable transport, targeting, and localization of ions, metabolites, proteins, and other macromolecules. They include channels that permit diffusion of specific ions or small molecules, carrier proteins or transporters that shuttle substrates by conformational changes, pumps that move substances against gradients using energy, and translocases that ferry polypeptides across membranes during protein targeting.

Examples of translocators span several families. Ion channels such as voltage-gated or ligand-gated channels allow rapid selective passage of ions. Carrier proteins, including the glucose transporters (GLUT family) and various solute carriers, mediate facilitated diffusion or secondary active transport. Pumps and ATPases, like the Na+/K+-ATPase and other P-type or ABC transporters, move substrates using energy from ATP hydrolysis. Translocases such as the SecYEG complex in bacteria and the TOM/TIM or TIC/TOC systems in mitochondria and chloroplasts move proteins across membranes during organelle biogenesis and protein trafficking. Nuclear transport receptors, including importins and exportins, shuttle proteins through the nuclear pore complex, while vesicle-associated systems coordinate cargo delivery between organelles.

Mechanistically, translocators operate via channels that permit diffusion, carriers that undergo alternating conformations to bind and release substrates, and pumps that couple transport to energy sources such as ATP or ion gradients. They play essential roles in physiology, enabling nutrient uptake, signal transduction, organelle biogenesis, and cellular homeostasis. Dysfunctions in translocators can contribute to a range of diseases, highlighting their importance in health and disease. See also translocon, transporter, channel, carrier protein, and nuclear transport.