Trans-Golgi network, transport vesicle

Membrane proteins inside transport vesicles bud off the endoplasmic reticulum on their way to the Golgi final sorting of many membrane proteins occurs in the trans-Golgi network. 

T. V. Kurzchalia, P. Dupree, R. G. Parton, R. Kellner, H. Virta, M. Lehnert, and K. Simons. VIP21, a 21-kD membrane protein is an integral component of trans-Golgi- network-derived transport vesicles. J. Cell Biol. 118 1003-1014(1992). 

Figure 1 The mode of action for bacterial AB-type exotoxins. AB-toxins are enzymes that modify specific substrate molecules in the cytosol of eukaryotic cells. Besides the enzyme domain (A-domain), AB-toxins have a binding/translocation domain (B-domain) that specifically interacts with a cell-surface receptor and facilitates internalization of the toxin into cellular transport vesicles, such as endosomes. In many cases, the B-domain mediates translocation of the A-domain into the cytosol by pore formation in cellular membranes. By following receptor-mediated endocytosis, AB-type toxins exploit normal vesicle traffic pathways into cells. One type of toxin escapes from early acidified endosomes (EE) into the cytosol, thus they are referred to as short-trip-toxins . In contrast, the long-trip-toxins take a retrograde route from early endosomes (EE) through late endosomes (LE), trans-Golgi network (TGN), and Golgi apparatus into the endoplasmic reticulum (ER) from where the A-domains translocate into the cytosol to modify specific substrates.

Figure 10-8 Current version of protein synthesis and processing via ER, Golgi, and secretory vesicles. CGN, ds-Golgi network C, T, M are the cis, medial, and trans compartments of the Golgi stack TGN, trans Golgi network. Arrows indicate some of the movements of transport vesicles.

Kinesin participates in vesicle transport in a number of cell types, including fast axonal transport in neurons (56). In Sertoli cells, kinesin has been observed to localize to the trans Golgi network, a location suggesting involvement in membrane trafficking within the cell (57). In addition, kinesin is localized to ectoplasmic specializations where it may be involved in the movement and positioning of elongate spermatids within the seminiferous epithelium (55). 

Transport vesicles transfer new membrane components (protein and lipids) and secretory products from the ER to the Golgi complex, from one Golgi cisterna to another, and from the trans-Golgi network to other organelles (e.g., lysosomes) or to the plasma membrane. 

As noted In the chapter Introduction, all eukaryotic cells continuously secrete certain proteins, a process commonly called constitutive secretion. Specialized secretory cells also store other proteins In vesicles and secrete them only when triggered by a specific stimulus. One example of such regulated secretion occurs In pancreatic p cells, which store newly made Insulin In special secretory vesicles and secrete Insulin In response to an elevation In blood glucose (see Figure 15-7). These and other secretory cells simultaneously utilize two different types of vesicles to move proteins from the trans-Golgi network to the cell surface regulated transport vesicles, often simply called secretory vesicles, and unregulated transport vesicles, also called constitutive secretory vesicles. 

The trans Golgi network (TGN) is a major branch point In the secretory pathway where soluble secreted proteins, lysosomal proteins, and In some cells membrane proteins destined for the basolateral or apical plasma membrane are segregated Into different transport vesicles. 

In polarized epithelial cells, membrane proteins destined for the apical or basolateral domains of the plasma membrane are sorted in the trans-Golgi network into different transport vesicles (see Figure 17-26). The GPI anchor is the only apical-basolateral sorting signal identified so far. 

Rab proteins 711 receptor-mediated endocytosis 728 regulated secretion 724 retrograde transport 715 sec mutants 706 secretory pathway 701 sorting signals 711 synaptotagmin 737 transc3rt osIs 727 trans-Golgi network (TGN) 701 transport vesicles 701 t SNAREs 708 v SNAREs 708... 

Kasai, K., Shin, H. W., Shinotsnka, C., Mnrakami, K., and Nakayama, K. (1999). Dynamin II is involved in endocytosis bnt not in the formation of transport vesicles from the trans-Golgi network. J. Biochem. (Tokyo) 125, 780-789. 

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