transGolgi

The trans-Golgi network (TGN) is the major sorting hub at the trans face of the Golgi apparatus in most eukaryotic cells. It collects proteins and lipids exiting the Golgi and directs them to appropriate destinations, including the plasma membrane, endosomes, lysosomes, and secretory granules.

It is not a single static compartment but a network of cisternae and tubular carriers that mature from the medial to the trans Golgi, forming carriers that bud off to deliver cargo. The TGN receives cargos from earlier Golgi compartments and sorts them according to signals such as sorting receptors and lipid domains.

The main pathways include secretory routes (both constitutive and regulated) to the plasma membrane or extracellular space; lysosomal targeting via mannose-6-phosphate receptors carrying hydrolytic enzymes to late endosomes and lysosomes; and sorting into secretory granules in endocrine or exocrine cells.

Molecular machinery involved in TGN sorting includes adaptor protein complexes (such as AP-1) and GGAs, clathrin-coated vesicles, and mechanisms for retrograde retrieval such as the retromer complex. Trafficking to target membranes is coordinated by Rab GTPases (for example Rab6 and Rab33) and by SNARE proteins that mediate membrane fusion with the correct destination.

Significance and context: proper TGN function is essential for regulated secretion, lysosome biogenesis, and presentation of membrane proteins. Disruptions in TGN sorting can impair cellular trafficking and are associated with various physiological and pathological states.