Abstract:
:Trimming of N-linked oligosaccharides by endoplasmic reticulum (ER) glucosidase II is implicated in quality control of protein folding. An alternate glucosidase II-independent deglucosylation pathway exists, in which endo-alpha-mannosidase cleaves internally the glucose-substituted mannose residue of oligosaccharides. By immunogold labeling, we detected most endomannosidase in cis/medial Golgi cisternae (83.8% of immunogold labeling) and less in the intermediate compartment (15.1%), but none in the trans-Golgi apparatus and ER, including its transitional elements. This dual localization became more pronounced under 15 degrees C conditions indicative of two endomannosidase locations. Under experimental conditions when the intermediate compartment marker p58 was retained in peripheral sites, endomannosidase was redistributed to the Golgi apparatus. Double immunogold labeling established a mutually exclusive distribution of endomannosidase and glucosidase II, whereas calreticulin was observed in endomannosidase-reactive sites (17.3% in intermediate compartment, 5.7% in Golgi apparatus) in addition to the ER (77%). Our results demonstrate that glucose trimming of N-linked oligosaccharides is not limited to the ER and that protein deglucosylation by endomannosidase in the Golgi apparatus and intermediate compartment additionally ensures that processing to mature oligosaccharides can continue. Thus, endomannosidase localization suggests that a quality control of N-glycosylation exists in the Golgi apparatus.
journal_name
Mol Biol Celljournal_title
Molecular biology of the cellauthors
Zuber C,Spiro MJ,Guhl B,Spiro RG,Roth Jdoi
10.1091/mbc.11.12.4227keywords:
subject
Has Abstractpub_date
2000-12-01 00:00:00pages
4227-40issue
12eissn
1059-1524issn
1939-4586journal_volume
11pub_type
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