ER/Golgi Intermediate Compartment

Appenzeller-Herzog C, Hauri HP (2006) The ER-Golgi intermediate compartment (ERGIC) in search of its identity and function. J Cell Sci 119 2173-21783... 

ERGIC ER-Golgi intermediate compartment HLH helix-loop-helix transcriptional regulator... 

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... 

The abbreviations for the predominant reaction are G, glucose M, mannose. All oligosaccharides terminate in a di-iV-acetylchitobiose sequence by which they are linked to Asn in the peptide chain. IC, intermediate compartment refers to the membranes interposed between the ER and Golgi complex. 

Glucosidase II has been shown by immunoelectron microscopy of hepatocytes to be located in the ER and transitional elements between the ER and Golgi complex [29], which have more recently been ascribed to the intermediate compartment [30], Furthermore, the enzyme has been detected in the nuclear envelope, but not in the Golgi apparatus [29, 30]. In contrast to glucosidase I, it has become evident that the glucosidase II is a soluble luminal or loosely associated membrane enzyme [31, 32] and indeed its catalytic subunit as determined from its cDNA does not contain a transmembrane domain, nor has an ER retention signal been found [33-35]. 

Hammond, C., and Helenius, A. Quality Control in the Secretory Pathway Retention of a Misfolded Viral Membrane Glycoprotein Involves Cycling bewteen the ER, Intermediate Compartment, and Golgi Apparatus J. Cell Biol. 1994 126, 41 52. 

GAA is synthesized as a 110 kDa precursor protein, which is core-glycosylated in the ER and acquires mannose 6-phosphate (M6P) residues in the Golgi as diagrammed in Fig. 10.1. In the lysosomal compartments, the precursor protein is processed to yield an intermediate 95 kDa form and the two mature, fully active, 76 and 70 kDa, forms of GAA (Reuser et al., 1995 Raben et al., 2002). The 110 kDa form is secreted and can be detected in the media of infected cells or serum of transduced animals and the remaining forms can be found in expressing cells. 

Modified LDL taken up by the cell are delivered to the endolysosome pathway, where enzymes hydrolyze cholesteryl esters to free cholesterol and fatty acids. The levels of free cholesterol and cholesteryl esters are regulated with the help of neutral cholesteryl ester hydrolase, which converts cholesteryl ester to free cholesterol. After cholesterol leaves the lysosome, it is transported to the ER and to the plasma membrane by means of an intermediate step through the Golgi apparatus. Recycling compartments, especially multivesicular endosomes, harbor most of the cholesterol in the endocytic pathway. The intra-endosomal membranes of multivesicular late endosomes that are enriched in the phospholipids lyso-bisphosphatidic acid/bismonoacylglycerophosphate serve as important regulators of cholesterol transport (Kobayashi et al. 1999 Ikonen 2008). Lysobisphosphatidic acid is structurally... 

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