AlgG is the periplasmic alginate-modifying enzyme in the KT2440 alginate biosynthesis cluster. By strong orthology to experimentally characterized Pseudomonas AlgG proteins, it epimerizes beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization, thereby helping generate the characteristic polymannuronate/MG-block architecture of Pseudomonas alginate. Direct KT2440 biochemistry is limited, but the reviewed UniProt entry, conserved cluster context, signal peptide, and ortholog literature support a confident assignment to periplasmic alginate biosynthesis. Ortholog studies also indicate that AlgG has a second non-catalytic role in the periplasmic secretion/protection complex that limits AlgL-mediated degradation of the polymer.
Definition: Catalysis of the polymer-level epimerization of beta-D-mannuronate residues in alginate to alpha-L-guluronate residues.
Justification: GO currently has alginic acid biosynthetic process and broad epimerase terms, but it lacks a specific molecular function term for the defining AlgG reaction (EC 5.1.3.37). This forces curators to use the generic carbohydrate epimerase parent and loses the polymer-level substrate specificity that distinguishes AlgG from small-molecule epimerases.
Parent term: racemase and epimerase activity, acting on carbohydrates and derivatives
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0042597
periplasmic space
|
IEA
GO_REF:0000044 |
ACCEPT |
Summary: This localization is well supported. AlgG carries an N-terminal signal peptide and lacks any mature transmembrane segment, and the experimentally characterized Pseudomonas AlgG orthologs function on the alginate polymer after it enters the periplasm.
Reason: The existing term is appropriately specific for a soluble or periplasm-associated catalytic step in alginate maturation. There is no evidence that AlgG itself is an inner-membrane enzyme.
Supporting Evidence:
file:PSEPK/algG/algG-deep-research-falcon.md
The mature enzyme is periplasmic: UniProt annotates a signal peptide at residues 1-25 and the catalytic chain from 26-519.
file:PSEPK/algG/algG-deep-research-falcon.md
AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
|
|
GO:0042121
alginic acid biosynthetic process
|
IEA
GO_REF:0000041 |
ACCEPT |
Summary: This process annotation should be retained. AlgG is the periplasmic modification enzyme that introduces guluronate residues into alginate and is part of the conserved alginate biosynthesis apparatus in Pseudomonas.
Reason: Even though direct KT2440 biochemistry is limited, ortholog studies and the reviewed UniProt entry clearly place AlgG within alginate biosynthesis rather than in a generic carbohydrate-isomerase pathway.
Supporting Evidence:
file:PSEPK/algG/algG-deep-research-falcon.md
AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
file:PSEPK/algG/algG-deep-research-falcon.md
AlgG sits in the conserved alginate biosynthesis cluster of KT2440 and is the most plausible source of guluronate formation during alginate production.
|
|
GO:0016857
racemase and epimerase activity, acting on carbohydrates and derivatives
|
ISS
file:PSEPK/algG/algG-deep-research-falcon.md |
NEW |
Summary: GOA currently misses the core molecular function of AlgG. The exact activity is mannuronan C5-epimerization at the polymer level; this broad carbohydrate epimerase term is the closest existing GO molecular function and should be added as a new annotation until GO contains a specific AlgG term.
Reason: UniProt assigns EC 5.1.3.37 and ortholog biochemistry defines the reaction precisely, but GO lacks a corresponding specific molecular function term for polymer-level mannuronan C5 epimerization.
Supporting Evidence:
file:PSEPK/algG/algG-deep-research-falcon.md
AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
file:PSEPK/algG/algG-deep-research-falcon.md
The Pseudomonas syringae AlgG structure shows a right-handed parallel beta-helix with a conserved DPHD motif, and His319 plus Arg345 are critical for catalysis.
file:PSEPK/algG/algG-deep-research-falcon.md
For KT2440 specifically, direct biochemical characterization is limited; functional assignment is based on strong orthology to experimentally characterized Pseudomonas AlgG proteins and conserved gene-cluster context.
|
Q: How important is AlgG's non-catalytic scaffolding role in KT2440 relative to its epimerase activity during native alginate production?
Suggested experts: Svein Valla, Dennis E. Ohman
Q: Under which physiological conditions does KT2440 deploy AlgG-dependent alginate remodeling most strongly?
Suggested experts: P. Lynne Howell, Martin Gimmestad
Experiment: Create an algG deletion strain and catalytic-site mutants in the DPHD motif, then compare polymer yield and uronate composition under alginate-inducing conditions.
Hypothesis: Catalytic-dead mutants will separate guluronate formation from the structural role of AlgG in polymer protection/export.
Experiment: Measure secreted alginate composition by NMR or linkage-sensitive enzymology in wild type, algG-null, and complemented strains.
Hypothesis: KT2440 AlgG introduces guluronate and MG patterning into alginate rather than producing long guluronate blocks.
Experiment: Test physical or genetic interactions between AlgG and AlgK, AlgX, AlgE, and AlgL in KT2440.
Hypothesis: AlgG participates in a periplasmic biosynthetic complex that channels alginate away from AlgL during export.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
UniProt Q88NC9 matches AlgG, a predicted mannuronan C5-epimerase (EC 5.1.3.37) from Pseudomonas putida KT2440; KT2440-specific literature also identifies algG as PP_1283 within the alginate biosynthetic cluster and reports its transcriptional induction under water-limiting conditions. However, no direct biochemical characterization of Q88NC9/KT2440 AlgG was found in the retrieved papers. Accordingly, the functional annotation for this protein is best scoped as a KT2440 locus supported by strain-specific transcriptomic evidence, with enzyme reaction, periplasmic localization, and pathway role inferred from closely related Pseudomonas AlgG ortholog studies rather than from a direct KT2440 enzyme assay (gulez2014colonymorphologyand pages 6-8, nilsson2011influenceofputative pages 1-2, franklin1994pseudomonasaeruginosaalgg pages 1-2, jain2003thedualroles pages 1-2, lynne2014catalyticmechanismand pages 1-2).
Blockquote: This blockquote verifies that Q88NC9 corresponds to P. putida KT2440 AlgG/PP_1283 and clearly distinguishes direct KT2440 evidence from orthology-based functional inference. It is useful for preventing overstatement in the final annotation.
Primary functional assignment: AlgG is a polymer-level mannuronan C5-epimerase (EC 5.1.3.37) that converts β-D-mannuronate (M) residues to α-L-guluronate (G) residues in the nascent alginate polymer during periplasmic transit, shaping alginate monomer composition and block structure. This activity is central to the alginate modification/export complex in pseudomonads and is strongly modulated by O-acetylation state of the substrate. (franklin1994pseudomonasaeruginosaalgg pages 1-2, jain2003thedualroles pages 1-2, lynne2014catalyticmechanismand pages 1-2)
Alginate is a linear, 1→4-linked copolymer of β-D-mannuronic acid (M) and its C5 epimer α-L-guluronic acid (G). In pseudomonads, alginate is synthesized initially as a polymannuronate (poly-M) chain and is subsequently modified in the periplasm by epimerization (AlgG) and acetylation (AlgF/AlgI/AlgJ/AlgX), with composition and substitutions affecting polymer properties and interactions (e.g., hydration, viscosity, gel behavior with cations). (ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2, roblesprice2004algxisa pages 2-3, wang2023strategytocombat pages 2-3)
AlgG catalyzes C5-epimerization at the uronic acid C5 stereocenter in polymeric alginate:
poly(β-D-mannuronate) → poly(β-D-mannuronate/α-L-guluronate)
Genetic and biochemical evidence from Pseudomonas aeruginosa shows algG mutants produce alginate lacking G residues, and expression of algG restores G incorporation, establishing AlgG as the enzyme introducing G residues into pseudomonad alginate. (franklin1994pseudomonasaeruginosaalgg pages 1-2, franklin1994pseudomonasaeruginosaalgg pages 7-7)
A central definitional distinction is that pseudomonads typically use a single periplasmic AlgG that introduces limited, patterned epimerization (predominantly M and alternating MG regions), whereas Azotobacter species encode multiple secreted AlgE family epimerases that can generate guluronate-rich G-blocks and are widely exploited for in vitro alginate tailoring. (lynne2014catalyticmechanismand pages 1-2, lynne2014catalyticmechanismand pages 10-12, tøndervik2020exploitingmannuronanc5 pages 1-3)
In P. putida KT2440, an alginate biosynthesis gene cluster spanning PP1277–PP1288 has been described, and algG is identified within this locus as PP_1283. (nilsson2011influenceofputative pages 1-2, gulez2014colonymorphologyand pages 6-8)
Under water limitation, whole-transcriptome profiling showed induction of multiple alginate genes in KT2440; specifically, algG (PP_1283) exhibited a log2 fold change of ~+0.44 in the wild type under water-limited versus water-replete conditions (reported as “alginate-C5-mannuronan-epimerase AlgG, putative”). (gulez2014colonymorphologyand pages 6-8)
Work in a closely related P. putida strain (mt-2) established that alginate is induced by matric (water-limiting) stress, where it contributes to a hydrated microenvironment and alters biofilm architecture; glycosyl composition analysis under matric stress detected mannuronic acid in EPS (consistent with alginate production) in wild type but not in an algD mutant. (chang2007alginateproductionby pages 1-2, chang2007alginateproductionby pages 4-5)
Biochemical assays show AlgG acts on polymeric poly-M substrates (“polymer-level” epimerase), and that O-acetylation of mannuronate residues strongly inhibits AlgG activity; chemical deacetylation of poly-M was required to detect strong epimerization, producing a nearly 10-fold increase in reactivity with a G-specific lyase readout compared with control reactions. (franklin1994pseudomonasaeruginosaalgg pages 7-8, franklin1994pseudomonasaeruginosaalgg pages 7-7)
This interplay is consistent with broader pathway understanding that acetylation during periplasmic transit can protect residues from epimerization and from certain alginate lyases, impacting both polymer composition and susceptibility to enzymatic remodeling. (ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2, ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7)
Direct localization evidence in P. aeruginosa indicates AlgG is synthesized as a signal-peptide-containing precursor (~60 kDa) and processed to a mature form (~55 kDa) that localizes to the periplasm. (franklin1994pseudomonasaeruginosaalgg pages 1-2)
Mechanistic synthesis and pathway models place AlgG as a periplasmic modifier acting on the polymer as it transits from the inner-membrane polymerase toward outer-membrane export. (roblesprice2004algxisa pages 2-3, ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4)
Structural/mechanistic work on periplasmic AlgG in Pseudomonas indicates:
- A single AlgG can epimerize roughly 22–44% of mannuronate residues in vivo in pseudomonads, producing polymers with polymannuronate segments and alternating MG sequences, rather than long G-blocks. (lynne2014catalyticmechanismand pages 1-2)
- AlgG requires relatively long substrates; a minimum of ~9 residues has been reported, with weak binding to a nonamer characterized by Ka ≈ 5.0 × 10^5 M−1. (lynne2014catalyticmechanismand pages 12-13)
- A processive/sliding mechanism and active-site geometry support the observation that pseudomonad alginate lacks G–G doublets in vivo (favoring alternating patterns). (lynne2014catalyticmechanismand pages 12-13)
Structural analysis supports a catalytic architecture in which a histidine (e.g., His319) is proposed as a catalytic base, Arg345 contributes to carboxylate neutralization (contrasting with Ca2+-mediated neutralization in many secreted AlgE enzymes), and water/solvent is implicated as the proton donor with possible positioning by Tyr314; a conserved DPHD motif is noted for AlgG-family periplasmic enzymes. (lynne2014catalyticmechanismand pages 1-2, lynne2014catalyticmechanismand pages 10-12, ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7)
In the pseudomonad model, Alg8 and Alg44 are implicated in polymerization, and the nascent chain is modified and routed through a periplasmic scaffold/complex involving AlgG, AlgX, and AlgK, and exits via the outer-membrane pore AlgE; the periplasmic lyase AlgL is co-expressed and implicated in clearing mislocalized polymer (and can degrade polymer if not properly shielded). (roblesprice2004algxisa pages 2-3, ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4)
A useful schematic model of this multi-protein system is shown in the retrieved figure. (ertesva¥g2015alginatemodifyingenzymesbiological media 3908e58c)
Genetic analysis in P. aeruginosa supports a dual role for AlgG: (i) epimerization (M→G) and (ii) assisting productive secretion by protecting the polymer from periplasmic AlgL-mediated degradation, potentially together with AlgK as part of a periplasmic scaffold guiding polymers to AlgE. (jain2003thedualroles pages 1-2)
A 2023 review on enzymatic biofilm dispersal highlights AlgG as the enzyme that epimerizes mannuronic to guluronic acid, affecting ManA/GulA composition and functional properties of alginate. It also compiles a wide reported range of alginate acetylation rates (4%–57%), emphasizing acetylation and epimer composition as determinants of cation-mediated gel behavior and material properties—parameters directly relevant to therapeutic biofilm disruption and biomaterials design. (wang2023strategytocombat pages 2-3)
A 2024 fermentation-oriented study engineered P. putida by deleting alginate-associated algA (among other genes), showing that targeting alginate production can reduce biofilm formation and improve cultivation characteristics. The engineered strain showed 40% lower biofilm formation after 72 h and increased cell densities in small bioreactors: 1.39×10^10 vs 6.4×10^9 CFU/mL (rich medium) and 6.11×10^9 vs 1.36×10^9 CFU/mL (mineral medium) for mutant versus wild type. While not specific to algG, the work explicitly lists algG among alginate pathway genes and demonstrates real-world process relevance of alginate-pathway engineering. (frolov2024constructionofthe pages 1-2)
A 2024 preprint reports detectable M→G epimerase side-activity in a gut bacterial alginate lyase with an (α/α)7-barrel fold, contrasting with the parallel β-helix folds typical of AlgG/AlgE epimerases. While this does not change AlgG’s annotation, it is relevant to “latest research” in that it suggests epimerization chemistry may be more widespread than previously recognized and may appear in enzymes annotated as lyases, expanding the search space for alginate-modifying enzymes. (tandrup2024theswissarmy pages 20-23)
Because alginate contributes to biofilm mechanical properties and antibiotic tolerance in pseudomonads, enzymatic strategies (e.g., exogenous polysaccharide-degrading enzymes) are used to weaken EPS matrices and sensitize bacteria; the 2023 review emphasizes extracellular enzymes as anti-biofilm tools due to accessibility and reduced reliance on cellular uptake. AlgG is indirectly relevant as the enzyme that sets alginate composition and thus influences matrix properties and response to enzymatic dispersal. (wang2023strategytocombat pages 2-3)
A practical approach to controlling alginate material properties is to tune guluronate content and block structure using epimerases. For example, applying Azotobacter mannuronan C5-epimerases increased G content from 32% to as high as 81%, and the G-rich oligomer drug candidate OligoG CF-5/20 is described as >85% G with DPn ~15–17, linking epimerization control to biomedical functionality (e.g., mucus rheology and biofilm disruption). While AlgG itself is periplasmic and not generally used as an extracellular processing enzyme, these data contextualize why the AlgG-catalyzed reaction is a key lever in alginate functional engineering. (tøndervik2020exploitingmannuronanc5 pages 1-3)
In P. putida (mt-2), alginate production under matric stress is positioned as an adaptive mechanism in water-limited habitats (soil-like conditions), shaping biofilm architecture and hydration microenvironments. This supports interpreting KT2440 alginate/algG induction under water limitation as part of a broader ecological stress-response strategy. (chang2007alginateproductionby pages 1-2, chang2007alginateproductionby pages 4-5, gulez2014colonymorphologyand pages 6-8)
An authoritative 2015 review synthesizes the prevailing model that bacterial alginate is synthesized as polymannuronate and then modified by periplasmic enzymes, with AlgG and AlgX described as integral components of a polymerization/export complex, and acetylation described as a key determinant of viscosity/water binding and as a protective modification against lyases and further epimerization. This view supports annotating AlgG not only as an epimerase but also as a component functionally coupled to secretion and periplasmic quality control. (ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2, ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4)
Key quantitative findings relevant to AlgG and alginate properties include:
- KT2440 expression: algG (PP_1283) log2 fold change ~+0.44 under water limitation (WT). (gulez2014colonymorphologyand pages 6-8)
- In vivo epimerization extent (Pseudomonas spp.): 22–44% of mannuronate residues epimerized by periplasmic AlgG. (lynne2014catalyticmechanismand pages 1-2)
- Biochemical assay (P. aeruginosa strains): FRD1 (AlgG+) 1.38 U vs algG mutant FRD462 0.28 U; complementation FRD462(pMF18) 1.46 U (units as A530-based readout after lyase assay). (franklin1994pseudomonasaeruginosaalgg pages 7-7)
- Acetylation range (compiled 2023 review): alginate acetylation reported 4%–57%. (wang2023strategytocombat pages 2-3)
- Substrate requirements (AlgG structural/mechanistic): minimum ~9 residues; Ka ≈ 5.0×10^5 M−1 for nonamer binding. (lynne2014catalyticmechanismand pages 12-13)
- Process implementation (2024 fermentation): engineered P. putida deletion strain showed 40% lower biofilm after 72 h and increased CFU/mL (rich: 1.39×10^10 vs 6.4×10^9; mineral: 6.11×10^9 vs 1.36×10^9). (frolov2024constructionofthe pages 1-2)
| Claim/topic | Key finding | Organism/strain studied | Evidence type | Citation (paper + year + DOI URL) |
|---|---|---|---|---|
| Reaction catalyzed | AlgG is a polymer-level mannuronan C5-epimerase that converts β-D-mannuronate (M) residues in alginate to α-L-guluronate (G) residues during alginate biosynthesis. | Pseudomonas aeruginosa | Genetic + biochemical | Franklin et al., 1994, https://doi.org/10.1128/jb.176.7.1821-1830.1994 (franklin1994pseudomonasaeruginosaalgg pages 1-2, franklin1994pseudomonasaeruginosaalgg pages 7-8) |
| Substrate specificity | AlgG acts on polymeric polymannuronate/poly-M rather than monomers; activity is detected on deacetylated polymer substrate. | P. aeruginosa | Biochemical | Franklin et al., 1994, https://doi.org/10.1128/jb.176.7.1821-1830.1994 (franklin1994pseudomonasaeruginosaalgg pages 7-8, franklin1994pseudomonasaeruginosaalgg pages 7-7) |
| Effect of acetylation on substrate use | O-acetylation strongly inhibits AlgG activity; chemical deacetylation of poly-M caused a nearly 10-fold increase in reactivity with a G-specific lyase after AlgG treatment. | P. aeruginosa | Biochemical | Franklin et al., 1994, https://doi.org/10.1128/jb.176.7.1821-1830.1994 (franklin1994pseudomonasaeruginosaalgg pages 7-8, franklin1994pseudomonasaeruginosaalgg pages 7-7) |
| Cellular localization | AlgG is synthesized with an N-terminal signal peptide, processed from an approximately 60-kDa precursor to an approximately 55-kDa mature protein, and localizes to the periplasm. | P. aeruginosa | Protein localization + sequence analysis | Franklin et al., 1994, https://doi.org/10.1128/jb.176.7.1821-1830.1994 (franklin1994pseudomonasaeruginosaalgg pages 1-2, franklin1994pseudomonasaeruginosaalgg pages 4-4) |
| Pathway role | In the Pseudomonas alginate biosynthesis/export complex, AlgG is a periplasmic modifier acting on nascent alginate as it passes from the inner-membrane polymerase machinery toward the outer-membrane export pore. | Pseudomonas spp. / P. aeruginosa model | Structural + pathway review | Ertesvåg, 2015, https://doi.org/10.3389/fmicb.2015.00523 (ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4, ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2); Robles-Price et al., 2004, https://doi.org/10.1128/jb.186.21.7369-7377.2004 (roblesprice2004algxisa pages 2-3, roblesprice2004algxisa pages 1-2) |
| Polymerization/export complex context | Alg8 and Alg44 are implicated in polymerization; AlgG, AlgX, and AlgK are periplasmic components; AlgE is the outer-membrane export pore; AlgL is a periplasmic lyase that degrades mislocalized polymer. Mutants lacking AlgG/AlgX/AlgK release degraded oligomers instead of polymer. | P. aeruginosa / Pseudomonas model | Genetic + review | Robles-Price et al., 2004, https://doi.org/10.1128/jb.186.21.7369-7377.2004 (roblesprice2004algxisa pages 2-3, roblesprice2004algxisa pages 1-2); Ertesvåg, 2015, https://doi.org/10.3389/fmicb.2015.00523 (ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4) |
| Dual functional role | Beyond epimerization, AlgG also helps protect nascent alginate from periplasmic AlgL-mediated degradation and supports productive secretion/polymer formation. | P. aeruginosa | Genetic | Jain et al., 2003, https://doi.org/10.1046/j.1365-2958.2003.03361.x (jain2003thedualroles pages 1-2) |
| Product composition in vivo | In Pseudomonas, a single periplasmic AlgG modifies about 22–44% of mannuronate residues, yielding polymers enriched in M and alternating MG regions rather than long G-blocks. | Pseudomonas spp. | Structural/mechanistic synthesis | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 1-2) |
| Block structure constraint | Processive action and active-site geometry imply that at most every other mannuronate can be epimerized, explaining alternating MG patterns and the absence of G-G doublets in vivo. | Pseudomonas spp. | Structural + mechanistic | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 12-13) |
| Quantitative genetic/biochemical rescue | G-specific lyase assay values were 1.38 activity units for wild type FRD1, 0.28 for the algG mutant FRD462, and 1.46 for complemented FRD462(pMF18), demonstrating loss and restoration of G incorporation. | P. aeruginosa strains FRD1 / FRD462 | Genetic complementation + biochemical assay | Franklin et al., 1994, https://doi.org/10.1128/jb.176.7.1821-1830.1994 (franklin1994pseudomonasaeruginosaalgg pages 7-7) |
| Minimum substrate length | Structural/mechanistic analysis indicates AlgG requires relatively long substrates, with a reported minimum of about 9 mannuronate residues for productive interaction. | Pseudomonas spp. (AlgG structural model from P. syringae) | Structural + mechanistic | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 12-13) |
| Binding affinity | AlgG binds a nonamer weakly, with reported association constant Ka approximately 5.0 × 10^5 M−1. | Pseudomonas spp. (AlgG structural model from P. syringae) | Structural + mechanistic | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 12-13) |
| Catalytic mechanism | Proposed catalytic residues include His319 as catalytic base, Arg345 for carboxylate neutralization, and a solvent-derived proton donor coordinated by Tyr314; AlgG carries a DPHD motif. | Pseudomonas syringae AlgG / Pseudomonas periplasmic AlgG family | Structural + mutational/mechanistic | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 1-2, lynne2014catalyticmechanismand pages 10-12, ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7) |
| Distinction from AlgE-type epimerases | AlgG is a single periplasmic Pseudomonas enzyme acting on nascent, largely unacetylated polymer and does not generate long G-block alginate in vivo; AlgE-type enzymes are extracellular/secreted, often multiple, Ca2+-dependent, and associated with G-block formation. | Pseudomonas vs Azotobacter / extracellular epimerase systems | Comparative structural + review | Lynne et al., 2014, publication URL not available in retrieved context (lynne2014catalyticmechanismand pages 1-2, lynne2014catalyticmechanismand pages 10-12); Ertesvåg, 2015, https://doi.org/10.3389/fmicb.2015.00523 (ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7) |
| Acetylation interplay | Acetylation by AlgF/AlgI/AlgJ during periplasmic transit increases water binding and viscosity and protects alginate from many lyases and from further epimerization, limiting accessible AlgG/epimerase targets. | Pseudomonads / bacterial alginate systems | Review | Ertesvåg, 2015, https://doi.org/10.3389/fmicb.2015.00523 (ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2, ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7, ertesva¥g2015alginatemodifyingenzymesbiological pages 2-3) |
Table: This table summarizes the strongest functional-annotation evidence for AlgG as a periplasmic mannuronan C5-epimerase in Pseudomonas alginate biosynthesis. It highlights reaction chemistry, substrate requirements, localization, pathway context, mechanism, and quantitative findings useful for annotating the PSEPK protein Q88NC9 by orthology-aware inference.
Within the retrieved corpus, there is no direct biochemical characterization of KT2440 AlgG (Q88NC9) (e.g., purified enzyme kinetics or structure). Therefore, mechanistic residues, binding constants, and localization are best treated as orthology-based inference from closely related Pseudomonas AlgG studies, while KT2440-specific claims should be limited to locus context and expression/phenotype studies. (gulez2014colonymorphologyand pages 6-8, franklin1994pseudomonasaeruginosaalgg pages 1-2, lynne2014catalyticmechanismand pages 1-2)
References
(gulez2014colonymorphologyand pages 6-8): Gamze Gulez, Ali Altıntaş, Mustafa Fazli, Arnaud Dechesne, Christopher T. Workman, Tim Tolker‐Nielsen, and Barth F. Smets. Colony morphology and transcriptome profiling of pseudomonas putida kt2440 and its mutants deficient in alginate or all eps synthesis under controlled matric potentials. MicrobiologyOpen, 3:457-469, Jun 2014. URL: https://doi.org/10.1002/mbo3.180, doi:10.1002/mbo3.180. This article has 33 citations and is from a peer-reviewed journal.
(nilsson2011influenceofputative pages 1-2): Martin Nilsson, Wen‐Chi Chiang, Mustafa Fazli, Morten Gjermansen, Michael Givskov, and Tim Tolker‐Nielsen. Influence of putative exopolysaccharide genes on pseudomonas putida kt2440 biofilm stability. Environmental microbiology, 13 5:1357-69, May 2011. URL: https://doi.org/10.1111/j.1462-2920.2011.02447.x, doi:10.1111/j.1462-2920.2011.02447.x. This article has 122 citations and is from a domain leading peer-reviewed journal.
(franklin1994pseudomonasaeruginosaalgg pages 1-2): Michael J. Franklin, E. 'CHETAN, Chitnis, Peter, Gacesa, Anders, Sonesson, David C. White, E. Dennis, and Ohman. Pseudomonas aeruginosa algg is a polymer level alginate c5-mannuronan epimerase. Journal of Bacteriology, 176:1821-1830, Apr 1994. URL: https://doi.org/10.1128/jb.176.7.1821-1830.1994, doi:10.1128/jb.176.7.1821-1830.1994. This article has 276 citations and is from a peer-reviewed journal.
(jain2003thedualroles pages 1-2): Sumita Jain, Michael J. Franklin, Helga Ertesvåg, Svein Valla, and Dennis E. Ohman. The dual roles of algg in c‐5‐epimerization and secretion of alginate polymers in pseudomonas aeruginosa. Molecular Microbiology, 47:1123-1133, Feb 2003. URL: https://doi.org/10.1046/j.1365-2958.2003.03361.x, doi:10.1046/j.1365-2958.2003.03361.x. This article has 116 citations and is from a domain leading peer-reviewed journal.
(lynne2014catalyticmechanismand pages 1-2): Catalytic mechanism and mode of action of the periplasmic alginate epimerase AlgG This article has 59 citations and is from a peer-reviewed journal.
(ertesva¥g2015alginatemodifyingenzymesbiological pages 1-2): Helga ErtesvÃ¥g. Alginate-modifying enzymes: biological roles and biotechnological uses. Frontiers in Microbiology, May 2015. URL: https://doi.org/10.3389/fmicb.2015.00523, doi:10.3389/fmicb.2015.00523. This article has 209 citations and is from a peer-reviewed journal.
(roblesprice2004algxisa pages 2-3): Antonette Robles-Price, Thiang Yian Wong, Håvard Sletta, Svein Valla, and Neal L. Schiller. Algx is a periplasmic protein required for alginate biosynthesis in pseudomonas aeruginosa. Journal of Bacteriology, 186:7369-7377, Nov 2004. URL: https://doi.org/10.1128/jb.186.21.7369-7377.2004, doi:10.1128/jb.186.21.7369-7377.2004. This article has 124 citations and is from a peer-reviewed journal.
(wang2023strategytocombat pages 2-3): Shaochi Wang, Yanteng Zhao, Alexandra P. Breslawec, Tingting Liang, Zhifen Deng, Laura L. Kuperman, and Qiuning Yu. Strategy to combat biofilms: a focus on biofilm dispersal enzymes. NPJ Biofilms and Microbiomes, Sep 2023. URL: https://doi.org/10.1038/s41522-023-00427-y, doi:10.1038/s41522-023-00427-y. This article has 204 citations and is from a peer-reviewed journal.
(franklin1994pseudomonasaeruginosaalgg pages 7-7): Michael J. Franklin, E. 'CHETAN, Chitnis, Peter, Gacesa, Anders, Sonesson, David C. White, E. Dennis, and Ohman. Pseudomonas aeruginosa algg is a polymer level alginate c5-mannuronan epimerase. Journal of Bacteriology, 176:1821-1830, Apr 1994. URL: https://doi.org/10.1128/jb.176.7.1821-1830.1994, doi:10.1128/jb.176.7.1821-1830.1994. This article has 276 citations and is from a peer-reviewed journal.
(lynne2014catalyticmechanismand pages 10-12): Catalytic mechanism and mode of action of the periplasmic alginate epimerase AlgG This article has 59 citations and is from a peer-reviewed journal.
(tøndervik2020exploitingmannuronanc5 pages 1-3): Anne Tøndervik, Olav A. Aarstad, Randi Aune, Susan Maleki, Philip D. Rye, Arne Dessen, Gudmund Skjåk-Bræk, and Håvard Sletta. Exploiting mannuronan c-5 epimerases in commercial alginate production. Marine Drugs, 18:565, Nov 2020. URL: https://doi.org/10.3390/md18110565, doi:10.3390/md18110565. This article has 23 citations.
(chang2007alginateproductionby pages 1-2): Woo-Suk Chang, Martijn van de Mortel, Lindsey Nielsen, Gabriela Nino de Guzman, Xiaohong Li, and Larry J. Halverson. Alginate production by pseudomonas putida creates a hydrated microenvironment and contributes to biofilm architecture and stress tolerance under water-limiting conditions. Nov 2007. URL: https://doi.org/10.1128/jb.00727-07, doi:10.1128/jb.00727-07. This article has 441 citations and is from a peer-reviewed journal.
(chang2007alginateproductionby pages 4-5): Woo-Suk Chang, Martijn van de Mortel, Lindsey Nielsen, Gabriela Nino de Guzman, Xiaohong Li, and Larry J. Halverson. Alginate production by pseudomonas putida creates a hydrated microenvironment and contributes to biofilm architecture and stress tolerance under water-limiting conditions. Nov 2007. URL: https://doi.org/10.1128/jb.00727-07, doi:10.1128/jb.00727-07. This article has 441 citations and is from a peer-reviewed journal.
(franklin1994pseudomonasaeruginosaalgg pages 7-8): Michael J. Franklin, E. 'CHETAN, Chitnis, Peter, Gacesa, Anders, Sonesson, David C. White, E. Dennis, and Ohman. Pseudomonas aeruginosa algg is a polymer level alginate c5-mannuronan epimerase. Journal of Bacteriology, 176:1821-1830, Apr 1994. URL: https://doi.org/10.1128/jb.176.7.1821-1830.1994, doi:10.1128/jb.176.7.1821-1830.1994. This article has 276 citations and is from a peer-reviewed journal.
(ertesva¥g2015alginatemodifyingenzymesbiological pages 6-7): Helga ErtesvÃ¥g. Alginate-modifying enzymes: biological roles and biotechnological uses. Frontiers in Microbiology, May 2015. URL: https://doi.org/10.3389/fmicb.2015.00523, doi:10.3389/fmicb.2015.00523. This article has 209 citations and is from a peer-reviewed journal.
(ertesva¥g2015alginatemodifyingenzymesbiological pages 3-4): Helga ErtesvÃ¥g. Alginate-modifying enzymes: biological roles and biotechnological uses. Frontiers in Microbiology, May 2015. URL: https://doi.org/10.3389/fmicb.2015.00523, doi:10.3389/fmicb.2015.00523. This article has 209 citations and is from a peer-reviewed journal.
(lynne2014catalyticmechanismand pages 12-13): Catalytic mechanism and mode of action of the periplasmic alginate epimerase AlgG This article has 59 citations and is from a peer-reviewed journal.
(ertesva¥g2015alginatemodifyingenzymesbiological media 3908e58c): Helga ErtesvÃ¥g. Alginate-modifying enzymes: biological roles and biotechnological uses. Frontiers in Microbiology, May 2015. URL: https://doi.org/10.3389/fmicb.2015.00523, doi:10.3389/fmicb.2015.00523. This article has 209 citations and is from a peer-reviewed journal.
(frolov2024constructionofthe pages 1-2): Mikhail Frolov, Galim Alimzhanovich Kungurov, Emil Elmirovich Valiakhmetov, Artur Sergeyevich Gogov, Natalia Viktorovna Trachtmann, and Shamil Zavdatovich Validov. Construction of the pseudomonas putida strain with low motility and reduced biofilm formation for application in fermentation. Fermentation, 10:606, Nov 2024. URL: https://doi.org/10.3390/fermentation10120606, doi:10.3390/fermentation10120606. This article has 2 citations.
(tandrup2024theswissarmy pages 20-23): Tobias Tandrup, José Pablo Rivas-Fernández, Mikkel Madsen, Mette E. Rønne, Agnes B. Petersen, Leesa J. Klau, Anne Tøndervik, Casper Wilkens, Finn L. Aachmann, Carme Rovira, and Birte Svensson. The swiss army knife of alginate manipulation – a gut bacterium alginate lyase with diverse catalytic activities. bioRxiv, Dec 2024. URL: https://doi.org/10.1101/2024.12.11.627697, doi:10.1101/2024.12.11.627697. This article has 0 citations.
(franklin1994pseudomonasaeruginosaalgg pages 4-4): Michael J. Franklin, E. 'CHETAN, Chitnis, Peter, Gacesa, Anders, Sonesson, David C. White, E. Dennis, and Ohman. Pseudomonas aeruginosa algg is a polymer level alginate c5-mannuronan epimerase. Journal of Bacteriology, 176:1821-1830, Apr 1994. URL: https://doi.org/10.1128/jb.176.7.1821-1830.1994, doi:10.1128/jb.176.7.1821-1830.1994. This article has 276 citations and is from a peer-reviewed journal.
(roblesprice2004algxisa pages 1-2): Antonette Robles-Price, Thiang Yian Wong, Håvard Sletta, Svein Valla, and Neal L. Schiller. Algx is a periplasmic protein required for alginate biosynthesis in pseudomonas aeruginosa. Journal of Bacteriology, 186:7369-7377, Nov 2004. URL: https://doi.org/10.1128/jb.186.21.7369-7377.2004, doi:10.1128/jb.186.21.7369-7377.2004. This article has 124 citations and is from a peer-reviewed journal.
(ertesva¥g2015alginatemodifyingenzymesbiological pages 2-3): Helga ErtesvÃ¥g. Alginate-modifying enzymes: biological roles and biotechnological uses. Frontiers in Microbiology, May 2015. URL: https://doi.org/10.3389/fmicb.2015.00523, doi:10.3389/fmicb.2015.00523. This article has 209 citations and is from a peer-reviewed journal.
id: Q88NC9
gene_symbol: algG
product_type: PROTEIN
status: DRAFT
aliases:
- PP_1283
taxon:
id: NCBITaxon:160488
label: Pseudomonas putida (strain ATCC 47054 / DSM 6125 / CFBP 8728 / NCIMB 11950 / KT2440)
description: >
AlgG is the periplasmic alginate-modifying enzyme in the KT2440 alginate
biosynthesis cluster. By strong orthology to experimentally characterized
Pseudomonas AlgG proteins, it epimerizes beta-D-mannuronate residues in
nascent alginate to alpha-L-guluronate after polymerization, thereby helping
generate the characteristic polymannuronate/MG-block architecture of
Pseudomonas alginate. Direct KT2440 biochemistry is limited, but the reviewed
UniProt entry, conserved cluster context, signal peptide, and ortholog
literature support a confident assignment to periplasmic alginate
biosynthesis. Ortholog studies also indicate that AlgG has a second
non-catalytic role in the periplasmic secretion/protection complex that limits
AlgL-mediated degradation of the polymer.
existing_annotations:
- term:
id: GO:0042597
label: periplasmic space
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: >
This localization is well supported. AlgG carries an N-terminal signal
peptide and lacks any mature transmembrane segment, and the
experimentally characterized Pseudomonas AlgG orthologs function on the
alginate polymer after it enters the periplasm.
action: ACCEPT
reason: >
The existing term is appropriately specific for a soluble or
periplasm-associated catalytic step in alginate maturation. There is no
evidence that AlgG itself is an inner-membrane enzyme.
supported_by:
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: "The mature enzyme is periplasmic: UniProt annotates a signal peptide at residues 1-25 and the catalytic chain from 26-519."
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
- term:
id: GO:0042121
label: alginic acid biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000041
review:
summary: >
This process annotation should be retained. AlgG is the periplasmic
modification enzyme that introduces guluronate residues into alginate and
is part of the conserved alginate biosynthesis apparatus in Pseudomonas.
action: ACCEPT
reason: >
Even though direct KT2440 biochemistry is limited, ortholog studies and
the reviewed UniProt entry clearly place AlgG within alginate
biosynthesis rather than in a generic carbohydrate-isomerase pathway.
supported_by:
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG sits in the conserved alginate biosynthesis cluster of KT2440 and is the most plausible source of guluronate formation during alginate production.
- term:
id: GO:0016857
label: racemase and epimerase activity, acting on carbohydrates and derivatives
evidence_type: ISS
original_reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
review:
summary: >
GOA currently misses the core molecular function of AlgG. The exact
activity is mannuronan C5-epimerization at the polymer level; this broad
carbohydrate epimerase term is the closest existing GO molecular
function and should be added as a new annotation until GO contains a
specific AlgG term.
action: NEW
reason: >
UniProt assigns EC 5.1.3.37 and ortholog biochemistry defines the
reaction precisely, but GO lacks a corresponding specific molecular
function term for polymer-level mannuronan C5 epimerization.
supported_by:
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: The Pseudomonas syringae AlgG structure shows a right-handed parallel beta-helix with a conserved DPHD motif, and His319 plus Arg345 are critical for catalysis.
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: For KT2440 specifically, direct biochemical characterization is limited; functional assignment is based on strong orthology to experimentally characterized Pseudomonas AlgG proteins and conserved gene-cluster context.
core_functions:
- molecular_function:
id: GO:0016857
label: racemase and epimerase activity, acting on carbohydrates and derivatives
directly_involved_in:
- id: GO:0042121
label: alginic acid biosynthetic process
locations:
- id: GO:0042597
label: periplasmic space
description: >
Best available existing GO representation of AlgG's core function. AlgG is
the periplasmic polymer-level mannuronan C5-epimerase that converts
mannuronate residues in nascent alginate to guluronate during alginate
biosynthesis.
supported_by:
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: "The mature enzyme is periplasmic: UniProt annotates a signal peptide at residues 1-25 and the catalytic chain from 26-519."
proposed_new_terms:
- proposed_name: mannuronan C5-epimerase activity
proposed_definition: >
Catalysis of the polymer-level epimerization of beta-D-mannuronate residues
in alginate to alpha-L-guluronate residues.
justification: >
GO currently has alginic acid biosynthetic process and broad epimerase
terms, but it lacks a specific molecular function term for the defining
AlgG reaction (EC 5.1.3.37). This forces curators to use the generic
carbohydrate epimerase parent and loses the polymer-level substrate
specificity that distinguishes AlgG from small-molecule epimerases.
proposed_parent:
id: GO:0016857
label: racemase and epimerase activity, acting on carbohydrates and derivatives
supported_by:
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: AlgG converts beta-D-mannuronate residues in nascent alginate to alpha-L-guluronate after polymerization at the inner membrane.
- reference_id: file:PSEPK/algG/algG-deep-research-falcon.md
supporting_text: GO currently misses the core molecular function of AlgG.
suggested_questions:
- question: How important is AlgG's non-catalytic scaffolding role in KT2440 relative to its epimerase activity during native alginate production?
experts:
- Svein Valla
- Dennis E. Ohman
- question: Under which physiological conditions does KT2440 deploy AlgG-dependent alginate remodeling most strongly?
experts:
- P. Lynne Howell
- Martin Gimmestad
suggested_experiments:
- description: Create an algG deletion strain and catalytic-site mutants in the DPHD motif, then compare polymer yield and uronate composition under alginate-inducing conditions.
hypothesis: Catalytic-dead mutants will separate guluronate formation from the structural role of AlgG in polymer protection/export.
- description: Measure secreted alginate composition by NMR or linkage-sensitive enzymology in wild type, algG-null, and complemented strains.
hypothesis: KT2440 AlgG introduces guluronate and MG patterning into alginate rather than producing long guluronate blocks.
- description: Test physical or genetic interactions between AlgG and AlgK, AlgX, AlgE, and AlgL in KT2440.
hypothesis: AlgG participates in a periplasmic biosynthetic complex that channels alginate away from AlgL during export.
references:
- id: GO_REF:0000041
title: Gene Ontology annotation based on UniPathway vocabulary mapping
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
findings: []
- id: UniProt:Q88NC9
title: UniProtKB/Swiss-Prot reviewed entry for ALGG_PSEPK (Q88NC9)
findings:
- statement: Reviewed entry identifies AlgG as mannuronan C5-epimerase (EC 5.1.3.37)
- statement: Signal peptide residues 1-25 and mature chain residues 26-519 support periplasmic localization
- statement: UniProt places AlgG in alginate biosynthesis and notes protection of nascent alginate from AlgL
- id: PMID:12534463
title: Complete genome sequence and comparative analysis of the metabolically versatile Pseudomonas putida KT2440
full_text_unavailable: true
findings:
- statement: Establishes PP_1283 as the KT2440 algG locus in the genome sequence
- id: PMID:12775688
title: The Pseudomonas fluorescens AlgG protein, but not its mannuronan C-5-epimerase activity, is needed for alginate polymer formation
full_text_unavailable: true
findings:
- statement: algG deletion caused AlgL-dependent degradation products instead of normal polymer
- statement: Catalytically inactive AlgG could still support polymer formation, implying a structural role in the biosynthetic complex
- id: PMID:24398681
title: Catalytic Mechanism and Mode of Action of the Periplasmic Alginate Epimerase AlgG
full_text_unavailable: true
findings:
- statement: Structural and mutational analysis identified His319 and Arg345 as key catalytic residues
- statement: AlgG is a processive periplasmic polymer-level epimerase with an electropositive substrate-binding groove
- id: file:PSEPK/algG/algG-deep-research-falcon.md
title: Falcon deep research fallback report for algG
findings:
- statement: KT2440 assignment is supported by strong orthology and conserved gene-cluster context
- statement: Periplasmic localization and alginate-biosynthetic role are the strongest defensible GO claims for KT2440