Temporal Association of the N- andO-Linked Glycosylation Events and Their Implication in the Polarized Sorting of Intestinal Brush Border Sucrase-Isomaltase, Aminopeptidase N, and Dipeptidyl Peptidase IV*
- From the Department of Physiological Chemistry, School of Veterinary Medicine Hannover, Bünteweg 17, D-30559 Hannover, Germany
Abstract
The temporal association betweenO-glycosylation and processing of N-linked glycans in the Golgi apparatus as well as the implication of these events in the polarized sorting of three brush border proteins has been the subject of the current investigation. O-Glycosylation of pro-sucrase-isomaltase (pro-SI), aminopeptidase N (ApN), and dipeptidyl peptidase IV (DPPIV) is drastically reduced when processing of the mannose-rich N-linked glycans is blocked by deoxymannojirimycin, an inhibitor of the Golgi-located mannosidase I. By contrast, O-glycosylation is not affected in the presence of swainsonine, an inhibitor of Golgi mannosidase II. The results indicate that removal of the outermost mannose residues by mannosidase I from the mannose-rich N-linked glycans is required before O-glycosylation can ensue. On the other hand, subsequent mannose residues in the core chain impose no sterical constraints on the progression of O-glycosylation. Reduction or modification of N- andO-glycosylation do not affect the transport of pro-SI, ApN, or DPPIV to the cell surface per se. However, the polarized sorting of two of these proteins, pro-SI and DPPIV, to the apical membrane is substantially altered when O-glycans are not completely processed, while the sorting of ApN is not affected. The processing of N-linked glycans, on the other hand, has no influence on sorting of all three proteins. The results indicate thatO-linked carbohydrates are at least a part of the sorting mechanism of pro-SI and DPPIV. The sorting of ApN implicates neitherO-linked nor N-linked glycans and is driven most likely by carbohydrate-independent mechanisms.
Footnotes
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↵* This work was supported by Grant Na 331/1-2 from the Deutsche Forschungsgemeinschaft, Bonn/Germany (to H. Y. N.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom all correspondence should be addressed. Tel.: 49-511-953-8780; Fax: 49-511-953-8585; E-mail:hnaim{at}biochemie.tiho-hannover.de.
- Abbreviations:
- ER
-
endoplasmic reticulum
- TGN
-
trans-Golgi network
- SI
-
sucrase-isomaltase (all forms)
- pro-SI
-
uncleaved sucrase-isomaltase
- ApN
-
aminopeptidase N
- LPH
-
lactase-phlorizin hydrolase
- DPPIV
-
dipeptidyl peptidase IV
- dMM
-
deoxymannojirimycin
- mAb
-
monoclonal antibody
- endo H
-
endoglycosidase H
- endo F/GF
-
endoglycosidase F/N-glycopeptidase F
- TFMS
-
trifluoromethanesulfonic acid
- VIP36
-
36-kDa vesicular integral membrane protein
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- Received February 26, 1999.
- Revision received March 26, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
