Golgi transport

COPI vesicles mediate anterograde transport from the intermediate compartment to the Golgi, transport within the Golgi apparatus and retrograde transport back from the Golgi to the ER by the recruitment of soluble... 

COPI-coated vesicles mediate intra-Golgi transport and Golgi to ER retrograde transport. The coats of these vesicles do not show the geometric forms seen with clathrin coats and have a more complex protein composition [3]. Coat protein purification first lead to the identification of a complex composed of seven individual coat-protein subunits, known as COPI or coatomer. Some of these subunits bear a sequence similarity to clathrin adaptors. In addition, there is a small GTP-binding protein, Arfl, present on COPI-coated vesicles. 

How the Golgi apparatus maintains its polarized structure while molecules move from one compartment to another is still a matter of debate. Two models were originally proposed based on different experimental evidence (Fig. 9-5) the vesicular transport model and the cisternal maturation model. A third model known as the dual transport model combines elements from both vesicular transport and cisternal maturation models and can better explain intra-Golgi transport. 

Proteins associated with the PDZ ligand of the 5-HT4e receptor C-terminus are completely different from those that bind to the 5-HT4a receptors. They include the neuronal isoform of nitric oxide synthase (nNOS) and CIPP, two PDZ-domain-containing proteins, and Sec 23, which lacks any obvious PDZ domain (9). Sec 23 is a member of a protein complex designated as COPII, which is involved in the budding of vesicles from the endoplasmic reticulum (ER) and ER-to-Golgi transport of proteins. 

Several of the proteins of the Golgi transport system are AT-acetylated at either the amino terminal or the e-amino group of a lysine residue. Acylation may be either cotranslational or posttranslational. Amino terminal acylation protects the proteins from degradation, and various acylations are required for the assembly of multisubunit membrane proteins and transport of glycoproteins through the Golgi. 

ER lumen, followed by three different proteolytic processing reactions in the Golgi [28,33]. Mature ot-factor is then released into the culture supernatant upon fusion of post-Golgi transport vesicles with the plasma membrane. 

Presley JH, Cole NB, Schroer TA, Hirschberg K, Zaal KJM, Lippincott-Schwartz J. ER-to-Golgi transport visualized in living 41. cells. Nature 1997 389 81-85. 

SNAP-25 (synaptosomal-associated protein of 25kDa) is a 206 residue protein that lacks a classical transmembrane segment, but is bound to the cytosolic surface of the neuronal plasmalemma via pal-mitoylation of four cysteine residues located at the center of the molecule (Fig. 3) (Bennett and Scheller, 1994 Sudhof, 1995). SNAP-25 is required for axonal growth during development, and for nerve terminal plasticity in the mature nervous system (Osen-Sand et al., 1993). The tissue distribution of SNAP-25 is less well characterized than that of VAMP however, its presence in pancreatic cells (Jacobson et al., 1994 Sadoul et al., 1995) may indicate that it is also expressed outside the nervous system. A SNAP-25 related protein required for post-Golgi transport has been cloned from yeast (Brenwald efal., 1994). 

Choudhury A, Dominguez M, Puri V, et al. (2002) Rab proteins mediate Golgi transport of caveola-internalized glycosphingolipids and correct lipid trafficking in Niemann-Pick C cells. 1 Clin Invest 109 1541-1550... 

Iversen, T.G., Skretting, G., Llorente, A., Nicoziani, P., van Deurs, B. and Sandvig, K. (2001) Endosome to Golgi transport of ricin is independent of clathrin and of the Rab9- and Rabll-GTPases. Mol Biol Cell, 12, 2099-2107. 

Belden, W. J., and Barlowe, C. (1996). Erv25p, a component of COPII-coated vesicles, forms a complex with Emp24p that is required for efficient endoplasmic reticulum to Golgi transport. / Biol. Chem. 271, 26939-26946. 

B. Zhang, M.A. Cunningham, W.C. Nichols, et al. Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex. Nat. Genet. 2003 34(2) 220-225. 

Similarly, Rabl Is essential for ER-to-Golgi transport reactions to occur in cell-free extracts. Rabl GTP binds to a... 

Among the class C yeast sec mutants are strains that lack functional Sec 18 or Seel 7, the yeast counterparts of mammalian NSF and a-SNAP, respectively. When these class C mutants are placed at the nonpermissive temperature, they accumulate ER-to-Golgi transport vesicles when the cells are shifted to the lower, permissive temperature, the accumulated vesicles are able to fuse with the c/s-Golgi. 

The experiments described previously in which the transit of VSVG-GFP in cultured mammalian cells is followed by fluorescence microscopy (see Figure 17-2) provided insight into the intermediates in ER-to-Golgi transport. In some cells, small fluorescent vesicles containing VSVG-GFP could be seen to form from the ER, move less than 1 )xm, and... 

ER-to-Golgi Transport and Proteolytic Activation Control the Activity of SREBP Transcription Factors... 

Du, X., Kristiana, I., Wong, J., and Brown, A. J. Involvement of Akt in ER-to-Golgi transport of SCAP/SREBP a link between a key cell proliferative pathway and membrane synthesis. Mol Biol Cell 17 (2006) 2735-2745. 

Brefeldin A Antiviral/antifungal Blocks ER-to-Golgi transport Arfl... 

Exol Cultured cells Blocks ER-to-Golgi transport U nknown... 

Within the Golgi, enzymes are targeted for endosomes (and eventually lysosomes) by addition of mannose 6-phosphate residues that bind to mannose 6-phosphate receptor proteins in the Golgi membrane. The mannose 6-phosphate receptors together with their bound acid hydrolases are incorporated into the clathrin-coated Golgi transport vesicles and released. The transport vesicles lose their clathrin coat and then fuse with the late endosomal membrane. The acidity of the endosome releases the acid hydrolases from the receptors into the vesicle lumen. The receptors are eventually recycled back to the Golgi. 

Dascher, C., and Balch, W. E. (1994). Dominant inhibitory mutants of ARFl block endoplasmic reticulum to Golgi transport and trigger disassembly of the Golgi apparatus. J. Biol. Chem. 269,1437-1448. 

We have used the reconstitution of COPI transport vesicle formation on isolated rat-liver Golgi membranes as one approach to characterize the role of the cytoskeleton during protein transport (Chen et al, 2004, 2005 Fucini et al., 2000, 2002). The cell-free reconstitution of intra-Golgi transport and COPI vesicle assembly was developed in the laboratory of J. Rothman during the 1980s (Balch et al., 1984 Malhotra et al., 1989 Serafini et al., 1991). These studies helped establish that GTP-bound ARFl initiates COPI vesicle assembly by triggering the assembly of the... 

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