alg13 (SPAC56E4.02c; UniProt O14190) encodes the catalytic subunit Alg13 of the UDP-GlcNAc transferase, a cytosolic glycosyltransferase recruited to the ER by Alg14, which adds the second GlcNAc (beta-1,4) to GlcNAc-PP-dolichol. In the cytoplasmic phase of dolichol-linked oligosaccharide (Glc3Man9GlcNAc2-PP-Dol) assembly on the ER membrane, it adds the next sugar to the growing precursor that oligosaccharyltransferase transfers to nascent glycoproteins. Function is assigned by orthology to the S. cerevisiae ALG enzymes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: EC mapping. Reason: UniProt's curated function, catalytic-activity and subunit statements (by similarity, ECO:0000250; the ISO row transfers from S. cerevisiae ALG13, SGD:S000003015) describe alg13 as the glycosyltransferase-28 subunit that, with alg14, adds the second GlcNAc to GlcNAc-PP-dolichol; PANTHER places it in the N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase subfamily (PTHR12867:SF6). No S. pombe assay is cached; the activity is that of the Alg13-Alg14 heterodimer and rests on orthology. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway file:SCHPO/alg13/alg13-uniprot.txt Reaction=an N-acetyl-alpha-D-glucosaminyl-diphospho-di-trans,poly-cis- file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. file:SCHPO/alg13/alg13-uniprot.txt PTHR12867:SF6; N-ACETYLGLUCOSAMINYLDIPHOSPHODOLICHOL N-ACETYLGLUCOSAMINYLTRANSFERASE |
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | ISO GO_REF:0000024 | ACCEPT | Summary: Transfer from S. cerevisiae; Alg13-Alg14 together form the enzyme. Reason: UniProt's curated function, catalytic-activity and subunit statements (by similarity, ECO:0000250; the ISO row transfers from S. cerevisiae ALG13, SGD:S000003015) describe alg13 as the glycosyltransferase-28 subunit that, with alg14, adds the second GlcNAc to GlcNAc-PP-dolichol; PANTHER places it in the N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase subfamily (PTHR12867:SF6). No S. pombe assay is cached; the activity is that of the Alg13-Alg14 heterodimer and rests on orthology. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway file:SCHPO/alg13/alg13-uniprot.txt Reaction=an N-acetyl-alpha-D-glucosaminyl-diphospho-di-trans,poly-cis- file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. file:SCHPO/alg13/alg13-uniprot.txt PTHR12867:SF6; N-ACETYLGLUCOSAMINYLDIPHOSPHODOLICHOL N-ACETYLGLUCOSAMINYLTRANSFERASE |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000044 | ACCEPT | Summary: Mapping. Reason: Organelle claim holds by similarity: UniProt's curated subcellular location is endoplasmic reticulum (ECO:0000250), and the alg14 partner it heterodimerises with is the ER-membrane anchor. The record has no FT TRANSMEM or signal-peptide feature for alg13 itself (only FT CHAIN), consistent with a peripheral subunit on the cytosolic face, which is carried separately as GO:0098554. Not shown directly in S. pombe. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: Second step of LLO assembly. Reason: UniProt's curated function (by similarity, ECO:0000250; ISO from S. cerevisiae ALG13) places alg13 at the second step of the dolichol-linked oligosaccharide pathway, and the curated reaction is the GlcNAc-PP-dolichol to GlcNAc2-PP-dolichol step. No S. pombe mutant data is cached; the process rests on orthology. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway file:SCHPO/alg13/alg13-uniprot.txt Reaction=an N-acetyl-alpha-D-glucosaminyl-diphospho-di-trans,poly-cis- |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | ISO GO_REF:0000024 | ACCEPT | Summary: Second step of LLO assembly. Reason: UniProt's curated function (by similarity, ECO:0000250; ISO from S. cerevisiae ALG13) places alg13 at the second step of the dolichol-linked oligosaccharide pathway, and the curated reaction is the GlcNAc-PP-dolichol to GlcNAc2-PP-dolichol step. No S. pombe mutant data is cached; the process rests on orthology. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway file:SCHPO/alg13/alg13-uniprot.txt Reaction=an N-acetyl-alpha-D-glucosaminyl-diphospho-di-trans,poly-cis- |
| GO:0016758 hexosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: Generic InterPro-derived parent of the specific activity, which is already annotated. Reason: Correct but general. Glycosyltransferase 28 C-terminal domain and Alg13-like family membership (IPR007235, IPR039042), with UniProt's catalytic activity (EC 2.4.1.141) and by-similarity function (second step of the dolichol pathway), specify the hexosyltransferase as the GlcNAc-PP-dolichol N-acetylglucosaminyltransferase (GO:0004577), which the gene already carries. Family and by-similarity evidence; no S. pombe assay is cached. Proposed replacements: N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Reaction=an N-acetyl-alpha-D-glucosaminyl-diphospho-di-trans,poly-cis- dolichol + UDP-N-acetyl-alpha-D-glucosamine = an N,N'- diacetylchitobiosyl-diphospho-di-trans,poly-cis-dolichol + UDP + H(+) file:SCHPO/alg13/alg13-uniprot.txt InterPro; IPR039042; Alg13-like. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IC GO_REF:0000111 | ACCEPT | Summary: Subunit of the Alg13-Alg14 UDP-GlcNAc transferase complex. Reason: UniProt's curated subunit statement (by similarity, ECO:0000250) says alg13 heterodimerises with alg14 to form the functional enzyme, i.e. the UDP-N-acetylglucosamine transferase complex. Not shown directly in S. pombe. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IEA GO_REF:0000117 | ACCEPT | Summary: Subunit of the Alg13-Alg14 UDP-GlcNAc transferase complex. Reason: UniProt's curated subunit statement (by similarity, ECO:0000250) says alg13 heterodimerises with alg14 to form the functional enzyme, i.e. the UDP-N-acetylglucosamine transferase complex. Not shown directly in S. pombe. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. file:SCHPO/alg13/alg13-uniprot.txt Involved in protein N-glycosylation. Essential for the second step of the dolichol-linked oligosaccharide pathway |
| GO:0098554 cytoplasmic side of endoplasmic reticulum membrane | TAS PMID:9878760 The dolichol pathway of N-linked glycosylation. | ACCEPT | Summary: Cytoplasmic-face LLO assembly steps (before flipping), as reviewed for the dolichol pathway. Supporting Evidence: PMID:9878760 The oligosaccharide substrate for the N-linked protein glycosylation is assembled at the membrane of the endoplasmic reticulum. |
| GO:0098562 cytoplasmic side of membrane | IEA GO_REF:0000117 | TOO GENERAL | Summary: Generic cytoplasmic side of membrane; the cytoplasmic side of the ER membrane is accepted in this review. Reason: True but uninformative. Alg13 is a soluble subunit that acts with the ER membrane protein Alg14 (by similarity) in the second, cytosol-facing step of dolichol-linked oligosaccharide assembly at the ER membrane; this supports the accepted cytoplasmic side of endoplasmic reticulum membrane (GO:0098554), which entails this term. Support is by similarity and from a review of the yeast pathway; none of the quotes names the cytoplasmic face explicitly. Supporting Evidence: file:SCHPO/alg13/alg13-uniprot.txt Heterodimer with alg14 to form a functional enzyme. PMID:9878760 The oligosaccharide substrate for the N-linked protein glycosylation is assembled at the membrane of the endoplasmic reticulum. |
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