Proteins are transported from the Golgi apparatus to their final destinations through the secretory pathway and endomembrane system. Proteins are sorted into different kinds of transport vesicles, which bud from the trans Golgi network and deliver their contents to the appropriate cellular locations.Some proteins are carried from the Golgi apparatus to the plasma membrane by a constitutive secretory pathway and some proteins are transported to the cell surface by a distinct pathway of regulated secretion or are specifically targeted to other intracellular destinations, such as lysosomes in animal cells or vacuoles in yeast.
Proteins are sorted into the regulated secretory pathway in thetrans Golgi network, where they are packaged into specialized secretory vesicles. These immature secretory vesicles are larger than the transport vesicles, often fuses with each other while further processing their protein contents. The sorting of proteins into the regulated secretory pathway appears to involve the recognition of signal patches shared by multiple proteins that enter this pathway.
In the process of selective transport of proteins to lysosomes, the lumenal lysosomal proteins are marked by mannose-6-phosphates that are formed by modification of their N-linked oligosaccharides shortly after entry into the Golgi apparatus. A specific receptor in the membrane of the trans Golgi network then recognizes these mannose-6-phosphate residues. The resulting complexes of receptor with the lysosomal enzymes are packaged into transport vesicles destined for lysosomes.
