Hamster UDP-N-acetylglucosamine: dolichol-P N-acetylglucosamine-1-P transferase has multiple transmembrane spans and a critical cytosolic loop

Ning Dan, Rachel B. Middleton, Mark A. Lehrman

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) is an endoplasmic reticulum (ER) enzyme responsible for synthesis of GlcNAc-P-P-dolichol, the committed step of dolichol-P-P-oligosaccharide synthesis. The sequence of hamster GPT predicted multiple transmembrane segments (Zhu, X., and Lehrman, M. A. (1990) J. Biol. Chem. 265, 14250-14255). GPT has also been predicted to act on the cytosolic face of the ER membrane, based on topological studies of its substrates and products. In this report we test these predictions by: (i) immunofluorescence microscopy with antibodies specific for native GPT sequences or epitope tags inserted into GPT, after selective permeabilization of the plasma membrane with digitonin; (ii) insertion of Factor Xa cleavage sites; (iii) in vitro translation of GPT; and (iv) site-directed mutagenesis. The loops between the 1st and 2nd and between the 9th and 10th predicted transmembrane spans of GPT were found to be cytosolic. In contrast, the loop between the 6th and 7th transmembrane spans, as well as the carboxyl terminus, were lumenal. Thus, hamster GPT must cross the ER membrane at least three times, consistent with previous computer-assisted predictions. There was no apparent N-glycosylation or signal sequence cleavage detected by in vitro translation. The cytosolic loop between the 9th and 10th transmembrane spans is the largest hydrophilic segment in GPT and, as judged by site- directed mutagenesis, has a number of conserved residues essential for activity. Hence, these results directly support the hypothesis that dolichol- P-P-oligosaccharide assembly is initiated in the cytosol and that a downstream intermediate must translocate to the lumenal face of the ER membrane.

Original languageEnglish (US)
Pages (from-to)30717-30724
Number of pages8
JournalJournal of Biological Chemistry
Volume271
Issue number48
DOIs
StatePublished - 1996

Fingerprint

Uridine Diphosphate N-Acetylglucosamine
Dolichol
Uridine Diphosphate
Acetylglucosamine
Transferases
Cricetinae
Endoplasmic Reticulum
Mutagenesis
Site-Directed Mutagenesis
Membranes
Oligosaccharides
Glycosylation
N-acetylglucopyranosylamine
Digitonin
Factor Xa
Cell membranes
Protein Sorting Signals
Fluorescence Microscopy
Cytosol
Epitopes

ASJC Scopus subject areas

  • Biochemistry

Cite this

Hamster UDP-N-acetylglucosamine : dolichol-P N-acetylglucosamine-1-P transferase has multiple transmembrane spans and a critical cytosolic loop. / Dan, Ning; Middleton, Rachel B.; Lehrman, Mark A.

In: Journal of Biological Chemistry, Vol. 271, No. 48, 1996, p. 30717-30724.

Research output: Contribution to journalArticle

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abstract = "UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) is an endoplasmic reticulum (ER) enzyme responsible for synthesis of GlcNAc-P-P-dolichol, the committed step of dolichol-P-P-oligosaccharide synthesis. The sequence of hamster GPT predicted multiple transmembrane segments (Zhu, X., and Lehrman, M. A. (1990) J. Biol. Chem. 265, 14250-14255). GPT has also been predicted to act on the cytosolic face of the ER membrane, based on topological studies of its substrates and products. In this report we test these predictions by: (i) immunofluorescence microscopy with antibodies specific for native GPT sequences or epitope tags inserted into GPT, after selective permeabilization of the plasma membrane with digitonin; (ii) insertion of Factor Xa cleavage sites; (iii) in vitro translation of GPT; and (iv) site-directed mutagenesis. The loops between the 1st and 2nd and between the 9th and 10th predicted transmembrane spans of GPT were found to be cytosolic. In contrast, the loop between the 6th and 7th transmembrane spans, as well as the carboxyl terminus, were lumenal. Thus, hamster GPT must cross the ER membrane at least three times, consistent with previous computer-assisted predictions. There was no apparent N-glycosylation or signal sequence cleavage detected by in vitro translation. The cytosolic loop between the 9th and 10th transmembrane spans is the largest hydrophilic segment in GPT and, as judged by site- directed mutagenesis, has a number of conserved residues essential for activity. Hence, these results directly support the hypothesis that dolichol- P-P-oligosaccharide assembly is initiated in the cytosol and that a downstream intermediate must translocate to the lumenal face of the ER membrane.",
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T2 - dolichol-P N-acetylglucosamine-1-P transferase has multiple transmembrane spans and a critical cytosolic loop

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N2 - UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) is an endoplasmic reticulum (ER) enzyme responsible for synthesis of GlcNAc-P-P-dolichol, the committed step of dolichol-P-P-oligosaccharide synthesis. The sequence of hamster GPT predicted multiple transmembrane segments (Zhu, X., and Lehrman, M. A. (1990) J. Biol. Chem. 265, 14250-14255). GPT has also been predicted to act on the cytosolic face of the ER membrane, based on topological studies of its substrates and products. In this report we test these predictions by: (i) immunofluorescence microscopy with antibodies specific for native GPT sequences or epitope tags inserted into GPT, after selective permeabilization of the plasma membrane with digitonin; (ii) insertion of Factor Xa cleavage sites; (iii) in vitro translation of GPT; and (iv) site-directed mutagenesis. The loops between the 1st and 2nd and between the 9th and 10th predicted transmembrane spans of GPT were found to be cytosolic. In contrast, the loop between the 6th and 7th transmembrane spans, as well as the carboxyl terminus, were lumenal. Thus, hamster GPT must cross the ER membrane at least three times, consistent with previous computer-assisted predictions. There was no apparent N-glycosylation or signal sequence cleavage detected by in vitro translation. The cytosolic loop between the 9th and 10th transmembrane spans is the largest hydrophilic segment in GPT and, as judged by site- directed mutagenesis, has a number of conserved residues essential for activity. Hence, these results directly support the hypothesis that dolichol- P-P-oligosaccharide assembly is initiated in the cytosol and that a downstream intermediate must translocate to the lumenal face of the ER membrane.

AB - UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT) is an endoplasmic reticulum (ER) enzyme responsible for synthesis of GlcNAc-P-P-dolichol, the committed step of dolichol-P-P-oligosaccharide synthesis. The sequence of hamster GPT predicted multiple transmembrane segments (Zhu, X., and Lehrman, M. A. (1990) J. Biol. Chem. 265, 14250-14255). GPT has also been predicted to act on the cytosolic face of the ER membrane, based on topological studies of its substrates and products. In this report we test these predictions by: (i) immunofluorescence microscopy with antibodies specific for native GPT sequences or epitope tags inserted into GPT, after selective permeabilization of the plasma membrane with digitonin; (ii) insertion of Factor Xa cleavage sites; (iii) in vitro translation of GPT; and (iv) site-directed mutagenesis. The loops between the 1st and 2nd and between the 9th and 10th predicted transmembrane spans of GPT were found to be cytosolic. In contrast, the loop between the 6th and 7th transmembrane spans, as well as the carboxyl terminus, were lumenal. Thus, hamster GPT must cross the ER membrane at least three times, consistent with previous computer-assisted predictions. There was no apparent N-glycosylation or signal sequence cleavage detected by in vitro translation. The cytosolic loop between the 9th and 10th transmembrane spans is the largest hydrophilic segment in GPT and, as judged by site- directed mutagenesis, has a number of conserved residues essential for activity. Hence, these results directly support the hypothesis that dolichol- P-P-oligosaccharide assembly is initiated in the cytosol and that a downstream intermediate must translocate to the lumenal face of the ER membrane.

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