Physical interactions between the Alg1, Alg2, and Alg11 mannosyltransferases of the endoplasmic reticulum

Gao, Xiao‐Dong; Nishikawa, Akiko; Dean, Neta

doi:10.1093/glycob/cwh072

Cited by 77 publications

(62 citation statements)

References 29 publications

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“…3A), suggesting stronger interaction of hAlg1p with itself than with hAlg2p or hAlg11p. Furthermore, this observation is completely in accordance with physical interactions among yeast Alg1p, Alg2p, and Alg11p, which were detected with our co-immunoprecipitation experiments (20). Taken together, we found that these mannosyltransferases can associate with each other to form an MT complex that includes hAlg1p, hAlg2p, and hAlg11p in a ratio of 2:1:1, respectively.…”

Section: C-1 Halg7p Halg14p and Halg13p Form A Gpt/nagt Complexsupporting

confidence: 90%

Physical Interactions among Human Glycosyltransferases Involved in Dolichol-Linked Oligosaccharide Biosynthesis

Takahashi¹,

Gao²

2012

TIGG

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In eukaryotic glycoproteins, the N-glycan plays an important role with respect to both their structure and function. On the rough endoplasmic reticulum (rER) membrane, the N-glycan precursor is biosynthesized as a dolichol-linked oligosaccharide (DLO), which consists of fourteen sugars linked to pyrophosphoryl-dolichol. For completion of fulllength DLO (Glc 3 Man 9 GlcNAc 2 -PP-dolichol), activities of at least eleven glycosyltransferases localized on the rER membrane are essential. Although twelve human genes for these enzymes have been identified, any physical interactions among them have not yet been systematically analyzed. In this review, we describe several physical interactions among them that were uncovered using the yeast split-ubiquitin system. Moreover, on the basis of observations obtained by this technique, novel models for networking among human glycosyltransferases can be proposed.

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Section: C-1 Halg7p Halg14p and Halg13p Form A Gpt/nagt Complexsupporting

confidence: 90%

Physical Interactions among Human Glycosyltransferases Involved in Dolichol-Linked Oligosaccharide Biosynthesis

Takahashi¹,

Gao²

2012

TIGG

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“…Recently, a number of other ER glycosyltransferases, namely Alg1, Alg2 and Alg11, which catalyze several steps of LLO biosynthesis on the cytosolic face of the ER have been shown to interact as hetero-oligomeric complexes that are important for their glycosyltransferase activity (32). We have not determined the stoichiometry of Alg13 and Alg14 within the hetero-oligomer nor have we ruled out the possibility that there may be additional interactions between Alg13 and Alg14with these or other ER proteins that may modify the activity of the UDP-GlcNAc transferase activity.…”

Section: Discussionmentioning

confidence: 99%

Alg14 Recruits Alg13 to the Cytoplasmic Face of the Endoplasmic Reticulum to Form a Novel Bipartite UDP-N-acetylglucosamine Transferase Required for the Second Step of N-Linked Glycosylation

Gao

Tachikawa

Sato

et al. 2005

Journal of Biological Chemistry

114

106

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N-linked glycosylation requires the synthesis of an evolutionarily conserved lipid-linked oligosaccharide (LLO) precursor that is essential for glycoprotein folding and stability. Despite intense research, several of the enzymes required for LLO synthesis have not yet been identified. Here we show that two poorly characterized yeast proteins known to be required for the synthesis of the LLO precursor, GlcNAc 2 -PP-dolichol, interact to form an unusual hetero-oligomeric UDP-GlcNAc transferase. Alg13 contains a predicted catalytic domain, but lacks any membrane-spanning domains. Alg14 spans the membrane but lacks any sequences predicted to play a direct role in sugar catalysis. We show that Alg14 functions as a membrane anchor that recruits Alg13 to the cytosolic face of the ER, where catalysis of GlcNAc 2 -PP-dol occurs. Alg13 and Alg14 physically interact and under normal conditions, are associated with the ER membrane. Overexpression of Alg13 leads to its cytosolic partitioning, as does reduction of Alg14 levels. Concomitant Alg14 overproduction suppresses this cytosolic partitioning of Alg13, demonstrating that Alg14 is both necessary and sufficient for the ER localization of Alg13. Further evidence for the functional relevance of this interaction comes from our demonstration that the human ALG13 and ALG14 orthologues fail to pair with their yeast partners, but when co-expressed in yeast can functionally complement the loss of either ALG13 or ALG14. These results demonstrate that this novel UDP-GlcNAc transferase is a unique eukaryotic ER glycosyltransferase that is comprised of at least two functional polypeptides, one that functions in catalysis and the other as a membrane anchor.Asparagine (N)-glycosylation is an essential modification that regulates protein folding and stability. Prior to its attachment to protein, the oligosaccharide Glu 3 Man 9 GlcNAc 2 is assembled on the lipid carrier, dolichyl pyrophosphate (dol-PP), in the ER 2 (see Refs. 1-4 for review). The earliest steps of this lipid-linked oligosaccharide (LLO) synthesis begin on the cytoplasmic face of the ER. Seven sugars, (two N-acetylglucosamines and five mannoses) are sequentially added to dol-P to form Man 5 GlcNAc 2 -PP-dol by enzymes that have their catalytic domain on the cytosolic side of the ER membrane and use sugar nucleotide substrates (2, 5, 6). The enzymes that catalyze addition of the next seven sugars (four mannoses and three glucoses) do so within the lumen of the ER and use dolichol-linked sugar substrates (see Ref. 1 for review). Once assembled, this core oligosaccharide is transferred to protein by oligosaccharyltransferase through an N-glycosidic bond to an asparagine that is part of the Asn-X-(Ser/Thr) consensus sequence (7). Proteinlinked oligosaccharide is immediately modified by the removal of glucoses and mannose by ER glucosidases and mannosidases. Failure to properly synthesize, transfer, or modify the N-linked glycan results in glycoproteins that are recognized by the quality control systems that restrict these abe...

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“…The lipid-linked GlcNAc 2 Man 3 pentasaccharide serves as substrate for Alg11p that elongates the LLO by two a-1,2-linked Man residues (Cipollo et al 2001;O'Reilly et al 2006). Interestingly, the three cytoplasm-oriented mannosyltransferases also form a hetero-oligomeric complex (Gao et al 2004). This results in two biosynthetic platforms that are characterized by the nucleotide-activated sugar substrate: the UDP-GlcNAc utilizing Alg7p/Alg13p/Alg14p and the GDP-Man-dependent Alg1p/Alg2p/Alg11p complex.…”

Section: Initial Steps Of Llo Biosynthesis On the Cytoplasmic Side Ofmentioning

confidence: 99%

N-Linked Protein Glycosylation in the Endoplasmic Reticulum

Breitling

Aebi

2013

Cold Spring Harbor Perspectives in Biology

249

204

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The attachment of glycans to asparagine residues of proteins is an abundant and highly conserved essential modification in eukaryotes. The N-glycosylation process includes two principal phases: the assembly of a lipid-linked oligosaccharide (LLO) and the transfer of the oligosaccharide to selected asparagine residues of polypeptide chains. Biosynthesis of the LLO takes place at both sides of the endoplasmic reticulum (ER) membrane and it involves a series of specific glycosyltransferases that catalyze the assembly of the branched oligosaccharide in a highly defined way. Oligosaccharyltransferase (OST) selects the Asn-X-Ser/Thr consensus sequence on polypeptide chains and generates the N-glycosidic linkage between the side-chain amide of asparagine and the oligosaccharide. This ER-localized pathway results in a systemic modification of the proteome, the basis for the Golgi-catalyzed modification of the N-linked glycans, generating the large diversity of N-glycoproteome in eukaryotic cells. This article focuses on the processes in the ER. Based on the highly conserved nature of this pathway we concentrate on the mechanisms in the eukaryotic model organism Saccharomyces cerevisiae.

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Physical interactions between the Alg1, Alg2, and Alg11 mannosyltransferases of the endoplasmic reticulum

Cited by 77 publications

References 29 publications

Physical Interactions among Human Glycosyltransferases Involved in Dolichol-Linked Oligosaccharide Biosynthesis

Physical Interactions among Human Glycosyltransferases Involved in Dolichol-Linked Oligosaccharide Biosynthesis

Alg14 Recruits Alg13 to the Cytoplasmic Face of the Endoplasmic Reticulum to Form a Novel Bipartite UDP-N-acetylglucosamine Transferase Required for the Second Step of N-Linked Glycosylation

N-Linked Protein Glycosylation in the Endoplasmic Reticulum

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