algC (PA5322) encodes the bifunctional phosphomannomutase/phosphoglucomutase (PMM/PGM) of Pseudomonas aeruginosa, a 463-residue soluble monomer of the alpha-D-phosphohexomutase superfamily. Using a single active site it reversibly interconverts mannose 6-phosphate and alpha-D-mannose 1-phosphate (EC 5.4.2.8) and glucose 6-phosphate and alpha-D-glucose 1-phosphate (EC 5.4.2.2) with comparable catalytic efficiency, and also acts more slowly on ribose and 2-deoxyglucose phosphates. Catalysis requires Mg2+ bound by a metal-binding loop (Asp242, Asp244, Asp246) and the phosphorylated Ser108; the enzyme transfers its phosphoryl group to the substrate, the resulting hexose 1,6-bisphosphate intermediate rotates 180 degrees without leaving the active site, and the phosphate on the other carbon is returned to Ser108. His329 and Arg20 act as the general base and acid, and the C-terminal domain 4 closes over the active site on substrate binding. Activity is stimulated by glucose 1,6-bisphosphate. Mannose 1-phosphate made by AlgC is converted by AlgA (GDP-mannose pyrophosphorylase) to GDP-mannose, which feeds alginate (via AlgD), the common polysaccharide antigen (A-band) and the Psl exopolysaccharide. Glucose 1-phosphate made by AlgC is the precursor of UDP-glucose for the glucose residues of the lipopolysaccharide outer core and of dTDP-L-rhamnose for rhamnolipid and Psl. algC mutants lack detectable PMM and PGM activity and are defective in alginate, a complete LPS core and O antigen, rhamnolipid, Psl and Pel, so AlgC sits at the branch point that supplies sugar-phosphate precursors to most of the virulence-associated glycans of this pathogen. Transcription is activated by AlgR and is strongly increased in mucoid strains.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IDA PMID:23517223 Identification of an essential active-site residue in the Ξ±-... | ACCEPT | Summary: AlgC binds one Mg2+ per subunit at a metal-binding loop (Asp242, Asp244, Asp246) together with the phosphoryl group of Ser108; Mg2+ is the catalytically required cofactor, and crystal structures including the H329A mutant (PDB 4IL8, PMID:23517223) resolve the bound metal. Reason: Metal binding is directly observed in many crystal structures of this protein and Mg2+ dependence is established kinetically (PMID:8050998). Zn2+ can occupy the site in crystals but yields inactive enzyme, so Mg2+ is the physiological cofactor. The term is as specific as the evidence warrants and describes the essential cofactor of the catalytic site. The cached record for PMID:23517223 is abstract-only; the cofactor statement in UniProt is tied to this paper by ECO:0000269 and the curator read the full text. Supporting Evidence: file:PSEAE/algC/algC-uniprot.txt Binds 1 Mg(2+) ion per subunit (PubMed:23517223) PMID:8050998 Purified PMM/phosphoglucomutase (PGM) required Mg2+ for maximum activity PMID:16880541 a metal-binding loop which coordinates the Mg 2+ ion necessary for activity |
| GO:0000287 magnesium ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the alpha-D-phosphohexomutase conserved site (IPR016066), which spans the phosphoserine and the metal-binding residues. Consistent with the experimental Mg2+ binding of AlgC. Reason: The electronic inference agrees with direct structural and biochemical evidence for Mg2+ binding by this protein (see the IDA row), so it is accepted with the same action. Supporting Evidence: file:PSEAE/algC/algC-uniprot.txt Binds 1 Mg(2+) ion per subunit (PubMed:23517223) PMID:16880541 a metal-binding loop which coordinates the Mg 2+ ion necessary for activity |
| GO:0004614 phosphoglucomutase activity | IDA PMID:8050998 Purification and characterization of phosphomannomutase/phos... | ACCEPT | Summary: Purified recombinant AlgC interconverts glucose 1-phosphate and glucose 6-phosphate (Km for G1P 22 uM, kcat 3000 min-1), with catalytic efficiency for G1P about twofold higher than for mannose 1-phosphate. Reason: Direct enzymatic assay of the purified protein; phosphoglucomutase is one of the two core activities of this bifunctional enzyme and is corroborated by kinetic, structural and genetic studies (PMID:11716469, PMID:14725765, PMID:7515870). Supporting Evidence: PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. PMID:8050998 On the basis of Kcat/Km ratio, the catalytic efficiency for G1P was about twofold higher than that for M1P. PMID:14725765 High-resolution structures with glucose 1-phosphate, glucose 6-phosphate, mannose 1-phosphate, and mannose 6-phosphate show that the position of the phosphate group of each substrate is held constant by a conserved network of hydrogen bonds. |
| GO:0004614 phosphoglucomutase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic annotation from the curated EC 5.4.2.2 / RHEA:23536 reaction on the UniProt entry, which is itself backed by experimental evidence. Reason: Agrees with direct biochemical evidence for phosphoglucomutase activity of purified AlgC; same claim as the IDA and IMP rows. Supporting Evidence: PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. PMID:11716469 The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) is responsible for the formation of mannose 1-phosphate and glucose 1-phosphate in the human pathogenic bacterium Pseudomonas aeruginosa. |
| GO:0004614 phosphoglucomutase activity | IMP PMID:7515870 The Pseudomonas aeruginosa algC gene encodes phosphoglucomut... | ACCEPT | Summary: algC mutants of strains PAO1 and PAC1R have no detectable PGM activity, and the cloned algC gene complements an Escherichia coli pgm mutant. Reason: Loss of PGM activity in the mutant plus heterologous complementation of an E. coli pgm mutant establish that AlgC provides the cellular PGM activity of P. aeruginosa; consistent with the IDA evidence. Supporting Evidence: PMID:7515870 We show that, as expected, the algC mutant strains had no detectable phosphomannomutase activity and that neither algC strain had detectable phosphoglucomutase (PGM) activity. PMID:7515870 we transferred the cloned, intact P. aeruginosa algC gene to a pgm mutant of Escherichia coli and observed complementation of the pgm phenotype |
| GO:0004615 phosphomannomutase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference at node PTN002464904 in PANTHER family PTHR43771; AlgC itself is one of the experimentally characterized descendants used to place the node. Reason: AlgC sits inside the PTHR43771:SF2 phosphomannomutase/phosphoglucomutase subfamily, and the inherited phosphomannomutase activity is confirmed for AlgC by direct assay. Its presence among the WITH/FROM entries reflects its own experimental grounding, as expected for an IBA. Supporting Evidence: file:PSEAE/algC/algC-uniprot.txt SIMILARITY: Belongs to the phosphohexose mutase family. PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. |
| GO:0004615 phosphomannomutase activity | IDA PMID:8050998 Purification and characterization of phosphomannomutase/phos... | ACCEPT | Summary: Purified recombinant AlgC interconverts mannose 1-phosphate and mannose 6-phosphate (Km for M1P 17 uM, kcat 1350 min-1), with Mg2+ required for maximal activity. Reason: Direct assay of the purified enzyme; phosphomannomutase is a core activity of AlgC, supported further by the enzyme-substrate complexes with mannose 1-phosphate and mannose 6-phosphate (PMID:14725765) and by steady-state kinetics (PMID:11716469). Supporting Evidence: PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. PMID:8050998 The apparent Km values for M1P and G1P were 17 and 22 microM, respectively. PMID:11716469 The V/K values for mannose 6-phosphate and glucose 6-phosphate show that they are equally good substrates for the enzyme. |
| GO:0004615 phosphomannomutase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic annotation from the curated EC 5.4.2.8 / RHEA:11140 reaction on the UniProt entry, backed by experimental evidence. Reason: Same claim as the IDA, IMP and IBA rows and consistent with direct biochemical evidence. Supporting Evidence: PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. |
| GO:0004615 phosphomannomutase activity | IMP PMID:1903398 Characterization and regulation of the Pseudomonas aeruginos... | ACCEPT | Summary: A PMM-deficient alginate mutant carries an R420C (R421 in the initiator-Met numbering) point mutation in algC, identifying algC as the structural gene for phosphomannomutase. Reason: Loss of PMM activity is tied to a single missense mutation in algC. The cached record is abstract-only; the curator had the full text, and the activity is independently confirmed by direct assay (PMID:8050998) and by later mutagenesis of Arg421 (PMID:16595672). Supporting Evidence: PMID:1903398 DNA sequence analysis of a defective algC gene (algC') cloned from a mutant of P. aeruginosa that lacked PMM activity revealed one point mutation PMID:8050998 PMM and PGM activities could not be detected in nonmucoid algC mutant strain 8858 and in LPS-rough algC mutant strain AK1012 |
| GO:0004615 phosphomannomutase activity | IMP PMID:22513190 Synthesis of multiple Pseudomonas aeruginosa biofilm matrix ... | ACCEPT | Summary: Ma et al. used an in-frame algC deletion in PAO1 and trans complementation to show that AlgC is required for Psl, Pel, alginate and LPS; the paper describes AlgC as the bifunctional PMM/PGM that provides the sugar precursors. Reason: The phenotypes are consistent with loss of PMM (and PGM) activity, and PMM activity is independently established by direct assay (PMID:8050998). The paper does not itself assay enzyme activity, so the IMP is weaker than the IDA evidence, but the claim is correct and the curator is deferred to. Supporting Evidence: PMID:22513190 The algC gene encodes a bifunctional enzyme with phosphomannomutase (PMM) and phosphoglucomutase (PMG) activities that catalyse the conversion of Man-6-P and glucose-6-P (Glc-6-P) into Man-1-P and Glc-1-P respectively PMID:22513190 In addition, Psl production in the ΞalgC mutant was recovered by expression of algC in trans |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the alpha-D-phosphohexomutase domains. Correct, but very general for an enzyme whose pathway roles are established experimentally. Reason: AlgC's carbohydrate metabolism is specifically the synthesis of sugar-phosphate precursors for alginate and the LPS core. The gene already carries the more specific descendants GO:0042121 alginic acid biosynthetic process and GO:0009244 lipopolysaccharide core region biosynthetic process, both supported by mutant phenotypes, so the general term should be refined to them. Proposed replacements: alginic acid biosynthetic process lipopolysaccharide core region biosynthetic process Supporting Evidence: PMID:8050998 This evidence suggests that AlgC functions as PMM and PGM in vivo, converting phosphomannose and phosphoglucose in the biosynthesis of both alginate and LPS. |
| GO:0009103 lipopolysaccharide biosynthetic process | IEA GO_REF:0000041 | MODIFY | Summary: UniPathway mapping (UPA00030, lipopolysaccharide biosynthesis). AlgC supplies glucose 1-phosphate needed for the glucose residues of the LPS core; algC mutants make a truncated core. Reason: Correct but general. The specific, experimentally supported role is in the LPS core region (PMID:7515870), already carried by the gene as GO:0009244, a descendant of this term. Proposed replacements: lipopolysaccharide core region biosynthetic process Supporting Evidence: PMID:7515870 Our finding that the algC gene product has PGM activity and that strains with mutations in this gene produce a truncated LPS core suggests that the synthesis of glucose 1-phosphate is necessary in the biosynthesis of the P. aeruginosa LPS core. |
| GO:0009243 O antigen biosynthetic process | IMP PMID:22513190 Synthesis of multiple Pseudomonas aeruginosa biofilm matrix ... | KEEP AS NON CORE | Summary: Ma et al. restate that algC mutants cannot make the LPS O antigen and a complete core, and report reduced B-band LPS when alginate or Psl compete for AlgC-derived precursors. Reason: The O-antigen defect of algC mutants is real but indirect. B-band O antigen cannot be ligated to the truncated core of the mutant, and the A-band (common polysaccharide antigen, a D-rhamnose polymer) needs GDP-mannose-derived GDP-D-rhamnose, which depends on AlgC's mannose 1-phosphate. AlgC performs a precursor-supplying step upstream of O-antigen assembly rather than a step of O-antigen synthesis proper, so the annotation is kept as non-core. Supporting Evidence: PMID:22513190 algC mutants cannot synthesize the LPS O-antigen and a complete LPS core PMID:22513190 Likewise, when either alginate or Psl were overproduced, levels of B-band LPS decreased. |
| GO:0009243 O antigen biosynthetic process | IMP PMID:7515870 The Pseudomonas aeruginosa algC gene encodes phosphoglucomut... | KEEP AS NON CORE | Summary: algC mutants of serotype O5 (PAO1) and O3 (PAC1R) strains lack both O side chains and the A-band polysaccharide. Reason: Same claim as the other O-antigen row. The phenotype follows from AlgC supplying glucose 1-phosphate for the core (the O-antigen attachment site) and mannose 1-phosphate for the A-band sugar precursors, not from a step of O-antigen assembly, so the annotation is retained as non-core. Supporting Evidence: PMID:7515870 did not express lipopolysaccharide (LPS) O side chains or the A-band (common antigen) polysaccharide |
| GO:0009244 lipopolysaccharide core region biosynthetic process | IMP PMID:7515870 The Pseudomonas aeruginosa algC gene encodes phosphoglucomut... | ACCEPT | Summary: algC mutants produce LPS that migrates like core-glucose-deficient rough mutants, and the loss of PGM activity explains a block in glucose 1-phosphate, the precursor of the UDP-glucose used for the core glucose residues. Reason: AlgC is the sole source of PGM activity in P. aeruginosa and catalyses the glucose 6-phosphate to glucose 1-phosphate step that supplies the core glucose residues; the truncated-core phenotype and E. coli pgm complementation support a direct catalytic role in the pathway producing the LPS core. One of the two principal biological roles of the PGM activity. Supporting Evidence: PMID:7515870 Our finding that the algC gene product has PGM activity and that strains with mutations in this gene produce a truncated LPS core suggests that the synthesis of glucose 1-phosphate is necessary in the biosynthesis of the P. aeruginosa LPS core. PMID:7515870 The data presented here thus demonstrate that the algC gene is required for the synthesis of a complete LPS core in two strains with different LPS core and O side chain structures. |
| GO:0009298 GDP-mannose biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: UniPathway mapping (UPA00126, GDP-alpha-D-mannose biosynthesis; AlgC catalyses step 2 of 2 in alpha-D-mannose 1-phosphate formation from fructose 6-phosphate, after AlgA phosphomannose isomerase). Reason: AlgC's phosphomannomutase activity directly produces mannose 1-phosphate, the substrate that AlgA guanylylates to GDP-mannose; the enzyme therefore catalyses a step of GDP-mannose biosynthesis from fructose 6-phosphate. This is the specific process for the PMM activity. Supporting Evidence: file:PSEAE/algC/algC-uniprot.txt PATHWAY: Nucleotide-sugar biosynthesis; GDP-alpha-D-mannose biosynthesis; alpha-D-mannose 1-phosphate from D-fructose 6-phosphate: step 2/2. PMID:11716469 The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) is responsible for the formation of mannose 1-phosphate and glucose 1-phosphate in the human pathogenic bacterium Pseudomonas aeruginosa. |
| GO:0016868 intramolecular phosphotransferase activity | IEA GO_REF:0000120 | MODIFY | Summary: Superfamily-level mapping from the alpha-D-phosphohexomutase domains. Correct but generic. Reason: The specific intramolecular phosphotransferase activities of AlgC are phosphomannomutase (GO:0004615) and phosphoglucomutase (GO:0004614), both is_a children of this term, both already carried by the gene and both experimentally established. Proposed replacements: phosphomannomutase activity phosphoglucomutase activity Supporting Evidence: PMID:8050998 The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. |
| GO:0042121 alginic acid biosynthetic process | IMP PMID:1903398 Characterization and regulation of the Pseudomonas aeruginos... | ACCEPT | Summary: algC was identified through PMM-deficient alginate mutants; its promoter resembles those of the alginate genes algD and algR, carries an AlgR binding site, and is activated by AlgR. Reason: AlgC catalyses the second step of the alginate precursor pathway (fructose 6-phosphate to mannose 6-phosphate by AlgA, to mannose 1-phosphate by AlgC, to GDP-mannose by AlgA, to GDP-mannuronic acid by AlgD), and the PMM-deficient algC mutant is non-mucoid. AlgC therefore catalyses a step of alginate biosynthesis, and this is the principal biological role of its PMM activity. The cached abstract does not state the alginate phenotype itself; the curator had the full text, and the role is confirmed by PMID:8050998. Supporting Evidence: PMID:1903398 The algC promoter showed significant homology with the promoters of two other P. aeruginosa genes involved in alginate synthesis, algD and algR1. PMID:8050998 This evidence suggests that AlgC functions as PMM and PGM in vivo, converting phosphomannose and phosphoglucose in the biosynthesis of both alginate and LPS. |
| GO:0042121 alginic acid biosynthetic process | IMP PMID:22513190 Synthesis of multiple Pseudomonas aeruginosa biofilm matrix ... | ACCEPT | Summary: Ma et al. describe AlgC as the enzyme providing sugar precursors for alginate and show competition between alginate and Psl for AlgC-derived precursors in mucoid bacteria. Reason: Consistent with the established role of AlgC in alginate precursor synthesis (PMID:1903398, PMID:8050998); same claim and action as the other alginate row. Supporting Evidence: PMID:22513190 Here we demonstrated that AlgC, a key enzyme that provides sugar precursors for the synthesis of alginate and lipopolysaccharides (LPS) is also required for both Psl and Pel production. |
| GO:1901137 carbohydrate derivative biosynthetic process | IEA GO_REF:0000117 | MODIFY | Summary: ARBA association-rule annotation. Correct in that AlgC makes the sugar-phosphate precursors of nucleotide sugars, but very general. Reason: The nucleotide-sugar products that AlgC directly feeds are GDP-mannose (via mannose 1-phosphate and AlgA; GO:0009298, already carried) and UDP-alpha-D-glucose (via glucose 1-phosphate and the UDP-glucose pyrophosphorylase; GO:0120530). Both are is_a descendants of this term and are the specific processes for the PMM and PGM activities. Proposed replacements: GDP-mannose biosynthetic process UDP-alpha-D-glucose biosynthetic process Supporting Evidence: PMID:11716469 The enzyme phosphomannomutase/phosphoglucomutase (PMM/PGM) is responsible for the formation of mannose 1-phosphate and glucose 1-phosphate in the human pathogenic bacterium Pseudomonas aeruginosa. PMID:7515870 suggests that the synthesis of glucose 1-phosphate is necessary in the biosynthesis of the P. aeruginosa LPS core |
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Download this section (compressed HTML)Q: Should AlgC carry GO:0106236 rhamnolipid biosynthesis? The algC mutant lacks rhamnolipid (PMID:10481091), but the supporting step is glucose 1-phosphate supply to RmlA in dTDP-L-rhamnose synthesis; whether precursor-supplying enzymes upstream of dTDP-rhamnose receive this term should be settled by comparison with how RmlA-D are annotated.
Q: How does the cell partition AlgC-derived mannose 1-phosphate and glucose 1-phosphate among alginate, Psl, Pel, A-band LPS, the LPS core and rhamnolipid, given that AlgC is the only PMM/PGM activity detected?
Q: Does AlgC phosphorylation state (phospho-Ser108 versus dephospho-enzyme) or glucose 1,6-bisphosphate availability regulate flux into alginate in mucoid clinical isolates?
Experiment: Quantify intracellular mannose 1-phosphate, glucose 1-phosphate, GDP-mannose and UDP-glucose pools by LC-MS in wild-type, algC null and catalytically impaired (H329A, S108A) strains, in mucoid and non-mucoid backgrounds, to measure how AlgC activity limits each exopolysaccharide.
Type: targeted metabolomics with site-directed mutants
Experiment: Test whether the Pel defect of algC mutants reflects loss of a glucose-derived UDP-sugar precursor by supplementing or bypassing glucose 1-phosphate production (for example, heterologous pgm expression) in a Pel-inducible algC background.
Type: genetic complementation and polysaccharide quantification
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