ALG13 encodes the soluble catalytic subunit of the bipartite UDP-N-acetylglucosamine transferase (Alg13-Alg14; EC 2.4.1.141) of S. cerevisiae, an essential enzyme related to the C-terminal UDP-sugar-binding domain of bacterial MurG (glycosyltransferase family GT28, GT-B fold). Alg13p has no transmembrane segment and binds the donor UDP-GlcNAc; it is recruited to the cytoplasmic face of the ER membrane by the membrane anchor subunit Alg14p, and only the Alg13-Alg14 heterodimer is active. The complex transfers a second beta-1,4-linked GlcNAc to GlcNAc-PP-dolichol to form GlcNAc2-PP-dolichol (chitobiosyl-PP-Dol), the second step of N-glycan precursor assembly. Depletion of Alg13p causes accumulation of GlcNAc1-PP-Dol, N-glycosylation defects and growth arrest; a cytosolic pool of Alg13p not bound to Alg14p is catalytically inactive. Human ALG13 variants cause ALG13-CDG.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | IDA PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | ACCEPT | Summary: IDA contributes_to (Bickel et al. 2005): immunoprecipitated Alg13p forms GlcNAc2-PP-Dol only when Alg14p is present. The contributes_to qualifier correctly reflects that activity resides in the heterodimer. Supporting Evidence: PMID:16100113 Immunoprecipitating Alg13p from solubilized extracts resulted in the formation of GlcNAc(2)-PP-Dol but required Alg14p for activity PMID:16100113 The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol. |
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA via EC 2.4.1.141 / RHEA:23380 with qualifier 'enables'. The activity is correct for Alg13p, which carries the UDP-GlcNAc-binding catalytic domain, but the enzyme is only active with Alg14p; the curated experimental rows use contributes_to, which is the more accurate representation. Supporting Evidence: PMID:16100110 Alg13 contains a predicted catalytic domain, but lacks any membrane-spanning domains. PMID:18547528 This glycosyltransferase is unusual in that it is active only in the presence of a binding partner, Alg14. |
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | IMP PMID:15615718 Two proteins homologous to the N- and C-terminal domains of ... | ACCEPT | Summary: IMP contributes_to (Chantret et al. 2005): depletion of Alg13 abolishes UDP-GlcNAc transfer onto Dol-PP-GlcNAc in vitro. Supporting Evidence: PMID:15615718 In vitro studies demonstrate that these proteins are required for transfer of [3H]GlcNAc from UDP-[3H]GlcNAc onto dolichyl-PP-GlcNAc. |
| GO:0004577 N-acetylglucosaminyldiphosphodolichol N-acetylglucosaminyltransferase activity | IMP PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | ACCEPT | Summary: IMP contributes_to (Bickel et al. 2005): microsomes from ALG13-repressed cells cannot transfer GlcNAc to GlcNAc1-PP-Dol. Supporting Evidence: PMID:16100113 Immunoprecipitating Alg13p from solubilized extracts resulted in the formation of GlcNAc(2)-PP-Dol but required Alg14p for activity |
| GO:0005515 protein binding | IPI PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | REMOVE | Summary: IPI with Alg14 (P38242) from Gao et al. 2005. The Alg13-Alg14 interaction is real and essential, but 'protein binding' adds no functional information; it is fully captured by part_of UDP-N-acetylglucosamine transferase complex (GO:0043541). Removal does not mean the interaction is false. Reason: Uninformative MF term; complex membership already annotated. Supporting Evidence: PMID:16100110 Alg13 and Alg14 physically interact and under normal conditions, are associated with the ER membrane. |
| GO:0005634 nucleus | HDA PMID:14690591 Assigning function to yeast proteins by integration of techn... | KEEP AS NON CORE | Summary: HDA (Hazbun et al. 2003 integrated analysis of essential ORFs) detecting tagged Alg13 in the nucleus. Alg13p is a small soluble protein; a nuclear signal in high-throughput imaging probably reflects the unbound soluble pool. No nuclear function is known. Reason: High-throughput observation without functional support. |
| GO:0005737 cytoplasm | HDA PMID:14690591 Assigning function to yeast proteins by integration of techn... | ACCEPT | Summary: HDA (Hazbun et al. 2003 essential-ORF localisation study) for cytoplasm. Consistent: Alg13p is a peripheral protein on the cytoplasmic side of the ER and also has a soluble cytoplasmic pool. |
| GO:0005737 cytoplasm | IDA PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | ACCEPT | Summary: IDA (Gao et al. 2005): Alg13 partitions to the cytoplasm when overexpressed or when Alg14 is limiting; physiologically it is on the cytoplasmic face of the ER. Supporting Evidence: PMID:16100110 Overexpression of Alg13 leads to its cytosolic partitioning, as does reduction of Alg14 levels. PMID:16100110 We show that Alg14 functions as a membrane anchor that recruits Alg13 to the cytosolic face of the ER, where catalysis of GlcNAc2-PP-dol occurs. |
| GO:0005783 endoplasmic reticulum | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: HDA from the GFP localisation atlas (Huh et al. 2003); ER localisation consistent with Alg14-mediated recruitment. |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000044 | ACCEPT | Summary: IEA from UniProt SubCell SL-0095 (Endoplasmic reticulum). Correct. Supporting Evidence: PMID:16100110 Alg13 and Alg14 physically interact and under normal conditions, are associated with the ER membrane. |
| GO:0005829 cytosol | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | KEEP AS NON CORE | Summary: HDA from the SWAT-tag GFP library (Yofe et al. 2016). A soluble Alg13 pool exists, but it is the catalytically inactive fraction not bound to Alg14; the functional location is the cytoplasmic face of the ER membrane. Reason: Real but non-functional pool. |
| GO:0005829 cytosol | IDA PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | KEEP AS NON CORE | Summary: IDA (Bickel et al. 2005): Alg13p fractionates to both membrane and cytosol, but the cytosolic form is enzymatically inactive. Reason: The cytosolic pool is inactive; function is at the ER membrane. Supporting Evidence: PMID:16100113 localizes both to the membrane and cytosol; the latter form, however, is enzymatically inactive. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA for dolichol-linked oligosaccharide biosynthesis from PANTHER ALG13 node. Correct. Supporting Evidence: PMID:16100113 The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IDA PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | ACCEPT | Summary: IDA (Gao et al. 2005): Alg13-Alg14 forms the UDP-GlcNAc transferase making GlcNAc2-PP-Dol on the cytosolic face of the ER. Supporting Evidence: PMID:16100110 We show that Alg14 functions as a membrane anchor that recruits Alg13 to the cytosolic face of the ER, where catalysis of GlcNAc2-PP-dol occurs. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IDA PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | ACCEPT | Summary: IDA (Bickel et al. 2005): Alg13p immunoprecipitates synthesise GlcNAc2-PP-Dol when Alg14p is present. Supporting Evidence: PMID:16100113 Immunoprecipitating Alg13p from solubilized extracts resulted in the formation of GlcNAc(2)-PP-Dol but required Alg14p for activity |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:15615718 Two proteins homologous to the N- and C-terminal domains of ... | ACCEPT | Summary: IMP (Chantret et al. 2005): Alg13 depletion causes accumulation of Dol-PP-GlcNAc. Supporting Evidence: PMID:15615718 down-regulation of either causes growth retardation, reduced N-glycosylation of carboxypeptidase Y, and accumulation of dolichyl-PP-GlcNAc. |
| GO:0006488 dolichol-linked oligosaccharide biosynthetic process | IMP PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | ACCEPT | Summary: IMP (Bickel et al. 2005): ALG13 repression causes accumulation of GlcNAc1-PP-Dol and N-glycosylation defects. Supporting Evidence: PMID:16100113 Down-regulation of each gene led to a defect in protein N-glycosylation and an accumulation of GlcNAc(1)-PP-Dol in vivo |
| GO:0016758 hexosyltransferase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: IEA from InterPro IPR007235 (glycosyl transferase family 28 C-terminal) to hexosyltransferase activity. Correct but general. Reason: General parent of GO:0004577. |
| GO:0042802 identical protein binding | IPI PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | MARK AS OVER ANNOTATED | Summary: IPI self-interaction of Alg13 from Gao et al. 2005 (two-hybrid / co-purification). The functional enzyme is the Alg13-Alg14 heterodimer; no role for Alg13 homo-oligomers has been shown, and 'identical protein binding' does not describe a molecular activity. Reason: Uninformative binding term with no demonstrated functional relevance. |
| GO:0042802 identical protein binding | IPI PMID:18547528 Solution structure of Alg13: the sugar donor subunit of a ye... | MARK AS OVER ANNOTATED | Summary: IPI self-interaction attributed to the Alg13 NMR solution-structure paper (Wang et al. 2008). The paper characterises monomeric Alg13 binding UDP-GlcNAc and stresses that activity requires Alg14; a homo-interaction is not a functional property. Reason: Uninformative binding term; function is heteromeric with Alg14. Supporting Evidence: PMID:18547528 This glycosyltransferase is unusual in that it is active only in the presence of a binding partner, Alg14. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IBA GO_REF:0000033 | ACCEPT | Summary: IBA part_of UDP-N-acetylglucosamine transferase complex. Correct. Supporting Evidence: PMID:16100113 The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IEA GO_REF:0000117 | ACCEPT | Summary: IEA from ARBA for UDP-N-acetylglucosamine transferase complex. Correct. Supporting Evidence: PMID:16100113 The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IPI PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | ACCEPT | Summary: IPI (Gao et al. 2005): Alg13 and Alg14 form a hetero-oligomeric UDP-GlcNAc transferase. Supporting Evidence: PMID:16100110 interact to form an unusual hetero-oligomeric UDP-GlcNAc transferase |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IPI PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | ACCEPT | Summary: IPI with Alg14 (SGD:S000000274) from Gao et al. 2005. Correct. Supporting Evidence: PMID:16100110 interact to form an unusual hetero-oligomeric UDP-GlcNAc transferase PMID:16100110 Alg13 and Alg14 physically interact and under normal conditions, are associated with the ER membrane. |
| GO:0043541 UDP-N-acetylglucosamine transferase complex | IPI PMID:16100113 Biosynthesis of lipid-linked oligosaccharides in Saccharomyc... | ACCEPT | Summary: IPI with Alg14 from Bickel et al. 2005 (Alg13-myc co-fractionates with Alg14-ZZ). Correct. Supporting Evidence: PMID:16100113 The data suggest that Alg13p associates with Alg14p to a complex forming the active transferase catalyzing the biosynthesis of GlcNAc(2)-PP-Dol. |
| GO:0098548 cytoplasmic side of Golgi membrane | IDA PMID:16100110 Alg14 recruits Alg13 to the cytoplasmic face of the endoplas... | MODIFY | Summary: IDA 'cytoplasmic side of Golgi membrane' from Gao et al. 2005. The paper's own abstract states that Alg14 recruits Alg13 to the cytosolic face of the ER, where GlcNAc2-PP-Dol is made; nothing in it concerns the Golgi. The cytoplasmic-side concept is right but the organelle appears to be a term-selection slip; the correct term is cytoplasmic side of ER membrane. Reason: Same paper explicitly places Alg13 at the cytosolic face of the ER, not the Golgi. Proposed replacements: cytoplasmic side of endoplasmic reticulum membrane Supporting Evidence: PMID:16100110 We show that Alg14 functions as a membrane anchor that recruits Alg13 to the cytosolic face of the ER, where catalysis of GlcNAc2-PP-dol occurs. |
| GO:0098562 cytoplasmic side of membrane | IEA GO_REF:0000117 | MODIFY | Summary: IEA from ARBA 'cytoplasmic side of membrane'. Correct in essence but unspecific; the experimentally established membrane is the ER. Reason: Replace with the specific child term. Proposed replacements: cytoplasmic side of endoplasmic reticulum membrane Supporting Evidence: PMID:16100110 We show that Alg14 functions as a membrane anchor that recruits Alg13 to the cytosolic face of the ER, where catalysis of GlcNAc2-PP-dol occurs. |
Loading supporting content…
Download this section (compressed HTML)Q: Does the soluble, inactive Alg13 pool have a regulatory role (e.g. sensing UDP-GlcNAc or Alg14 availability), or is it simply excess protein?
Experiment: Quantify Alg13 partitioning between membrane and cytosol under different UDP-GlcNAc levels and growth conditions, and test whether the cytosolic pool is degraded or recruited on demand.
Catalytic component of UDP-GlcNAc transferase; required for the second step of dolichyl-linked oligosaccharide synthesis; anchored to the ER membrane via interaction with Alg14p; similar to bacterial and human glycosyltransferases; protein abundance increases in response to DNA replication stress; both human homologs ALG13 and ALG14 are required to complement yeast alg13 mutant
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)