MNS1 (At1g51590; also called AtMANIb or alpha-mannosidase IB) is one of two redundant Golgi class I alpha-1,2-mannosidases (glycoside hydrolase family 47) in Arabidopsis. It is a type II single-pass membrane protein with a short cytoplasmic tail, a signal-anchor transmembrane segment and a lumenal GH47 catalytic domain. It depends on Ca2+ or Mn2+. Recombinant MNS1 trims alpha-1,2-linked mannose residues from oligomannosidic N-glycans. It converts Man8GlcNAc2, the product of the ER/early-Golgi mannosidase MNS3, to Man5GlcNAc2, starting on the A-branch. From Man9GlcNAc2 it yields only Man6GlcNAc2, because it acts poorly on the terminal mannose of the B-branch. Together with its paralog MNS2 it produces the Man5GlcNAc2 substrate needed to make hybrid and complex plant N-glycans in the Golgi. Fluorescent fusions localize to Golgi stacks, and proteomic fractionation places it in early (cis) Golgi cisternae. Single mutants have normal glycans. mns1 mns2 double mutants accumulate Man8GlcNAc2 and lack complex N-glycans. They have root-growth and cell-wall defects that become severe under salt stress, when the abundance of glycoproteins such as the cellulose-related endoglucanase KORRIGAN/RSW2 falls. MNS1 is not needed for glycan-dependent ER-associated degradation, which in plants uses the ER-resident MNS4 and MNS5.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000137 Golgi cis cisterna | HDA PMID:31266899 Separating Golgi Proteins from Cis to Trans Reveals Underlyi... | ACCEPT | Summary: Cisternal-resolution proteomics (free-flow separation of early to late Golgi subcompartments) assigned MNS1 to the cis cisterna. This matches the early position of class I mannosidase trimming, before the medial/trans glycosyltransferases that build complex glycans. Reason: Fits the enzyme's place in the N-glycan maturation pathway. Its Man5GlcNAc2 product is the substrate for GnTI and later Golgi enzymes. The cached paper is abstract-only, so I cannot check the MNS1-specific assignment and defer to the TAIR curator. A cis-cisterna location is compatible with the experimentally established Golgi membrane residence. Supporting Evidence: PMID:31266899 we exploit differences in surface charge of intact cisternae to perform separation of early to late Golgi subcompartments PMID:19914916 Golgi alpha-mannosidase I hydrolases (MANI) are key enzymes that play a role in the early N-glycan modification pathway in the Golgi apparatus. |
| GO:0000139 Golgi membrane | EXP PMID:19914916 Two Arabidopsis thaliana Golgi alpha-mannosidase I enzymes a... | ACCEPT | Summary: AtMANIb (MNS1)-GFP/DsRed fusions were detected in Golgi stacks. MNS1 is a type II signal-anchor membrane protein whose catalytic domain faces the lumen. Reason: This is the core location. The experimental Golgi localization and the type II membrane topology together support Golgi membrane as the precise location. Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0000139 Golgi membrane | EXP PMID:20023195 Class I alpha-mannosidases are required for N-glycan process... | ACCEPT | Summary: Fluorescent MNS1 fusions localize to punctate mobile Golgi bodies. HΓΌttner et al. confirmed MNS1-FP labelling of the Golgi with the same constructs. Reason: Independent experimental support for the core Golgi membrane location. Supporting Evidence: PMID:20023195 All three MNS proteins were found to localize in punctate mobile structures reminiscent of Golgi bodies. PMID:24737672 In contrast with MNS1 ( Figure 2B ) and MNS3 ( Figure 2C ), there was no detectable labeling of downstream compartments like the Golgi apparatus. |
| GO:0000139 Golgi membrane | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT placed Golgi membrane at node PTN000201534, the Golgi class I mannosidase clade. Its experimental seeds include MNS1 (AT1G51590) itself, MNS2 (AT3G21160) and mouse Golgi Man1a1/Man1a2. Reason: MNS1 is inside the clade and supplies its own experimental evidence to the node, which is expected, not circular. The IBA adds that Golgi residence is inherited across plant and animal Golgi mannosidase I, not a plant-specific feature. Fly alpha-Man-Ia (same PANTHER subfamily SF6) descends from the same node. Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0000139 Golgi membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic mapping of the UniProt subcellular location (Golgi apparatus membrane). In this entry that location is backed by experimental evidence. Reason: Agrees with the experimental Golgi membrane annotations. Supporting Evidence: PMID:20023195 All three MNS proteins were found to localize in punctate mobile structures reminiscent of Golgi bodies. |
| GO:0004559 alpha-mannosidase activity | IDA PMID:19914916 Two Arabidopsis thaliana Golgi alpha-mannosidase I enzymes a... | MODIFY | Summary: Recombinant MNS1 hydrolysed alpha-mannosyl residues from Man8GlcNAc2 and Man9GlcNAc2, and the activity was sensitive to 1-deoxymannojirimycin. Reason: The activity is real, but the same assay shows the more specific activity on alpha-1,2-linked mannose of N-glycans (EC 3.2.1.113). Replace with GO:0004571, which the gene already carries by EXP and IBA. Proposed replacements: mannosyl-oligosaccharide 1,2-alpha-mannosidase activity Supporting Evidence: PMID:19914916 both AtMANI isoforms encode 1-deoxymannojirimycin-sensitive alpha-mannosidase I and act on Man(8)GlcNAc(2) and Man(9)GlcNAc(2) structures to yield Man(5)GlcNAc(2) |
| GO:0004559 alpha-mannosidase activity | IDA PMID:20023195 Class I alpha-mannosidases are required for N-glycan process... | MODIFY | Summary: Recombinant MNS1 removed three alpha-1,2-mannose residues from Man8GlcNAc2. Reason: The linkage and substrate are defined (alpha-1,2-mannose on oligomannosidic N-glycans), so the specific term GO:0004571 is warranted. Proposed replacements: mannosyl-oligosaccharide 1,2-alpha-mannosidase activity Supporting Evidence: PMID:20023195 MNS1/2 readily removed three alpha1,2-mannose residues from Man(8)GlcNAc(2) |
| GO:0004571 mannosyl-oligosaccharide 1,2-alpha-mannosidase activity | EXP PMID:19914916 Two Arabidopsis thaliana Golgi alpha-mannosidase I enzymes a... | ACCEPT | Summary: Recombinant MNS1 converted Man8GlcNAc2 to Man5GlcNAc2 (EC 3.2.1.113) and Man9GlcNAc2 to Man8GlcNAc2/Man6GlcNAc2 (EC 3.2.1.209). It was inhibited by kifunensine and 1-deoxymannojirimycin but not by swainsonine. Reason: The core molecular function, measured directly on the Arabidopsis protein. Supporting Evidence: PMID:19914916 both AtMANI isoforms encode 1-deoxymannojirimycin-sensitive alpha-mannosidase I and act on Man(8)GlcNAc(2) and Man(9)GlcNAc(2) structures to yield Man(5)GlcNAc(2) file:ARATH/MNS1/MNS1-uniprot.txt Produces Man(5)GlcNAc(2) from Man(8)GlcNAc(2), but only Man(6)GlcNAc(2) |
| GO:0004571 mannosyl-oligosaccharide 1,2-alpha-mannosidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT placed this activity at the PTHR11742 root node PTN000201533, seeded by many experimentally characterised GH47 enzymes, MNS1 among them. Reason: The activity is conserved across the class I alpha-mannosidase family and is experimentally established for MNS1 itself. MNS1's own appearance among the donors is expected. Supporting Evidence: PMID:20023195 MNS1/2 readily removed three alpha1,2-mannose residues from Man(8)GlcNAc(2) file:ARATH/MNS1/MNS1-uniprot.txt Belongs to the glycosyl hydrolase 47 family. |
| GO:0004571 mannosyl-oligosaccharide 1,2-alpha-mannosidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined electronic annotation from GH47 domain membership and the curated Rhea reactions/EC 3.2.1.113. Reason: Agrees with the experimental activity. Supporting Evidence: PMID:19914916 both AtMANI isoforms encode 1-deoxymannojirimycin-sensitive alpha-mannosidase I and act on Man(8)GlcNAc(2) and Man(9)GlcNAc(2) structures to yield Man(5)GlcNAc(2) |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: GH47 enzymes bind a catalytic Ca2+ ion in the active-site barrel. UniProt lists Ca2+ or Mn2+ as cofactor for MNS1, from enzyme assays, and a Ca2+-binding residue (position 529) by similarity. Reason: Metal binding is a real part of the catalytic mechanism but secondary to the mannosidase activity. Mn2+ can replace Ca2+, so calcium ion binding is not an independent function. Supporting Evidence: file:ARATH/MNS1/MNS1-uniprot.txt Note=Ca(2+) or Mn(2+). Mg(2+) can be used to a lesser extent. |
| GO:0005768 endosome | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | MARK AS OVER ANNOTATED | Summary: The LOPIT analysis classified MNS1 into a combined Golgi/TGN class. Endosome appears to come from the plant TGN/early-endosome identity, not from a separate endosomal assignment. Reason: The method cannot tell Golgi from TGN, and imaging shows MNS1 in Golgi stacks. A class I mannosidase acting early in N-glycan maturation is not expected to reside in endosomes, and no imaging study reports it there. Supporting Evidence: PMID:22923678 The Golgi apparatus and the TGN proteins were combined into one class because they have a similar fractionation profile. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: PAINT placed ER at the family root PTN000201533, seeded only by ER-type class I mannosidases (human MAN1B1, yeast Mns1, Htm1/Mnl1 and a Candida ortholog). MNS1 is in the Golgi clade PTN000201534, which carries a separate Golgi membrane IBD. Reason: MNS1 passes through the ER during biosynthesis, as any type II Golgi protein does, but it has never been seen to reside or act there. Fluorescent fusions label Golgi stacks, and its substrate, Man8GlcNAc2, is made by MNS3. The ER term fits the ancestral ER-type enzymes; for the Golgi clade it is an over-propagation from the root. The Golgi node's own IBD is the informative location. Propagation Review Root cause: PROPAGATION BAD Failure modes: COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000201533 SUPPORTS SOURCE BUT NOT TARGET Root IBD seeded only by ER-type class I mannosidases. MNS1 descends through the Golgi clade node PTN000201534, which carries a Golgi membrane IBD, and MNS1 has been detected only in Golgi stacks. Supporting Evidence: PMID:24737672 MNS1 and MNS2 are Golgi-Ξ±-mannosidases and display a redundant function during N -glycan trimming in Arabidopsis PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0005794 Golgi apparatus | HDA PMID:16618929 Mapping the Arabidopsis organelle proteome. | MODIFY | Summary: LOPIT density-gradient proteomics assigned MNS1 to the Golgi apparatus. Reason: Correct but less specific than the supported Golgi membrane (type II signal-anchor protein), which the gene already carries by EXP and IBA. Proposed replacements: Golgi membrane Supporting Evidence: PMID:16618929 enabling confident and simultaneous localization of 527 proteins to the endoplasmic reticulum, Golgi apparatus, vacuolar membrane, plasma membrane, or mitochondria and plastids |
| GO:0005794 Golgi apparatus | HDA PMID:22430844 Isolation and proteomic characterization of the Arabidopsis ... | MODIFY | Summary: MNS1 was identified in the purified Arabidopsis Golgi proteome. Reason: Correct; the more specific Golgi membrane is supported. Proposed replacements: Golgi membrane Supporting Evidence: PMID:22430844 A collection of 371 proteins consistently identified in all replicates has been proposed to represent the Golgi proteome |
| GO:0005794 Golgi apparatus | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | MODIFY | Summary: LOPIT classified MNS1 in the combined Golgi/TGN class. Reason: Correct; refine to Golgi membrane. Proposed replacements: Golgi membrane Supporting Evidence: PMID:22923678 The Golgi apparatus and the TGN proteins were combined into one class because they have a similar fractionation profile. |
| GO:0005794 Golgi apparatus | IDA PMID:19914916 Two Arabidopsis thaliana Golgi alpha-mannosidase I enzymes a... | MODIFY | Summary: MNS1 fluorescent fusions were seen in Golgi stacks. Reason: Correct; Golgi membrane is the precise supported term, given the type II signal-anchor topology. Proposed replacements: Golgi membrane Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0005794 Golgi apparatus | IDA PMID:20023195 Class I alpha-mannosidases are required for N-glycan process... | MODIFY | Summary: MNS1 fusions localize to punctate mobile Golgi bodies. Reason: Correct; refine to Golgi membrane. Proposed replacements: Golgi membrane Supporting Evidence: PMID:20023195 All three MNS proteins were found to localize in punctate mobile structures reminiscent of Golgi bodies. |
| GO:0005794 Golgi apparatus | ISM GO_REF:0000122 | MODIFY | Summary: AtSubP sequence-based prediction of Golgi localization. Reason: The prediction agrees with experiment; refine to Golgi membrane, as for the other Golgi apparatus rows. Proposed replacements: Golgi membrane Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0005802 trans-Golgi network | HDA PMID:22923678 Putative glycosyltransferases and other plant Golgi apparatu... | MARK AS OVER ANNOTATED | Summary: TGN comes from the LOPIT Golgi/TGN combined class, which does not separate the two compartments. Reason: Neither imaging nor cisternal proteomics puts MNS1 in the TGN. Imaging shows Golgi stacks, and the cisternal fractionation (PMID:31266899) puts it in the cis cisterna, at the opposite face of the stack from the TGN. The TGN call is an artifact of the merged classifier class. Supporting Evidence: PMID:22923678 The Golgi apparatus and the TGN proteins were combined into one class because they have a similar fractionation profile. |
| GO:0005886 plasma membrane | ISM GO_REF:0000122 | REMOVE | Summary: AtSubP sequence-based prediction of plasma membrane localization. Reason: Experiments contradict this prediction. MNS1 is a Golgi-resident type II membrane protein in imaging and in Golgi/cisternal proteomics. LOPIT, which has a plasma membrane class, did not assign it there. Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. PMID:20023195 All three MNS proteins were found to localize in punctate mobile structures reminiscent of Golgi bodies. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the six-hairpin glycosidase-like superfamily. Reason: True but very general. The supported process is N-glycan processing (GO:0006491), which the gene already carries by IMP/IGI. Proposed replacements: N-glycan processing Supporting Evidence: PMID:20023195 class I alpha-mannosidases are essential for early N-glycan processing |
| GO:0006491 N-glycan processing | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learning annotation to N-glycan processing. Reason: Agrees with the genetic and biochemical evidence for MNS1. Supporting Evidence: PMID:19914916 either AtMANIa or AtMANIb can function as the Golgi alpha-mannosidase I that produces the Man(5)GlcNAc(2) N-glycan structure necessary for complex N-glycan synthesis |
| GO:0006491 N-glycan processing | IGI PMID:19914916 Two Arabidopsis thaliana Golgi alpha-mannosidase I enzymes a... | ACCEPT | Summary: manIa manIb (mns2 mns1) double mutants accumulate Man8GlcNAc2 and lack complex and hybrid N-glycans; single mutants are like wild type. MNS1 and MNS2 are redundant. Reason: MNS1 performs a catalytic step of N-glycan processing (Man8 to Man5 trimming). This is participation, not just necessity, and the in vitro activity confirms it. Supporting Evidence: PMID:19914916 the manIa manIb double mutant lines produced Man(8)GlcNAc(2) as the predominant N-glycan and lacked plant-specific complex and hybrid N-glycans |
| GO:0006491 N-glycan processing | IMP PMID:20023195 Class I alpha-mannosidases are required for N-glycan process... | ACCEPT | Summary: mns1 mns2 double mutants accumulate Man8GlcNAc2, and mns1 mns2 mns3 triple mutants carry almost only Man9GlcNAc2. Reason: Core process, supported by direct glycan analysis of mutants together with the enzyme activity. Supporting Evidence: PMID:20023195 Man(8)GlcNAc(2) accumulation in the mns1 mns2 double mutant PMID:20023195 class I alpha-mannosidases are essential for early N-glycan processing |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping to membrane. Reason: Correct but general. The specific supported location is Golgi membrane (GO:0000139), which the gene already carries by EXP and IBA. Proposed replacements: Golgi membrane Supporting Evidence: PMID:19914916 In planta, AtMANI-GFP/DsRed fusion proteins were detected in the Golgi stacks. |
| GO:0036503 ERAD quality control pathway | IBA GO_REF:0000033 | REMOVE | Summary: PAINT placed ERAD at the family root PTN000201533. All of its seeds are ER-type or EDEM/Htm1-type enzymes; none comes from the Golgi clade PTN000201534 that contains MNS1. Reason: There is direct negative genetic evidence for the target in its own species. HΓΌttner et al. tested mns1 mns2 against two independent membrane-anchored ERAD substrates (BRI1-5, BRI1-9), and the dwarf phenotypes were not suppressed; the authors conclude MNS1-MNS3 are dispensable for this ERAD. The plant glycan degradation signal is made by ER-resident MNS4/MNS5. MNS1 is a Golgi enzyme of regular glycan maturation. The ERAD term belongs to the ER-type/EDEM branches and was over-propagated from the root to the Golgi clade. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000201533 SUPPORTS SOURCE BUT NOT TARGET Root ERAD IBD seeded by ER-type and EDEM/Htm1-type enzymes (yeast, fission yeast, mouse, human). No Golgi-clade member is a seed, and Arabidopsis mns1 mns2 does not affect ERAD of BRI1-5/BRI1-9 (PMID:24737672). Supporting Evidence: PMID:24737672 These data indicate that MNS4 and MNS5 are required for the turnover of the membrane-anchored ERAD substrates BRI1-5 and BRI1-9, whereas MNS1 to MNS3 are dispensable for this process. PMID:24737672 MNS1 to MNS3 appear dispensable for this ERAD process |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: PAINT places ER (GO:0005783) and ERAD (GO:0036503) at the PTHR11742 root, and they propagate into the Golgi clade (PTN000201534). Arabidopsis MNS1/MNS2 are experimentally dispensable for ERAD. Should these IBDs be blocked at the Golgi node?
Q: Isoform 2 (Q9C512-2) lacks residues 1-104, including the cytoplasmic tail and signal-anchor transmembrane segment. Is it expressed as a protein, and if so is it secreted or misrouted, and is it active?
Q: Plant MNS1 trims Man9GlcNAc2 only to Man6GlcNAc2, by a route distinct from mammalian MANI. Is this branch preference shared by insect SF6 members such as Drosophila alpha-Man-Ia, or is it specific to plants?
Experiment: Test single-residue variants of the predicted catalytic acid/base residues (positions 179, 312, 423, 445) and the Ca2+-binding residue 529 on recombinant MNS1. Use defined Man9 isomers to map which residues set the A-branch preference and the poor B-branch activity.
Experiment: Use cisternal-resolution imaging (e.g. super-resolution colocalization with cis and trans Golgi markers) of MNS1 expressed from its native promoter, to confirm the cis cisterna assignment and rule out residence in the TGN or early endosome.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)