pelA (PA3064) encodes PelA, a large periplasmic, multidomain enzyme that modifies the Pel exopolysaccharide of Pseudomonas aeruginosa. Pel is a cationic, partially deacetylated alpha-1,4-linked N-acetylgalactosamine polymer that acts as an intercellular adhesin in the biofilm matrix, in part by cross-linking extracellular DNA. PelA is encoded by the first gene of the pelA-pelG operon. It has an N-terminal glycoside hydrolase domain (GH166, GH114-like TIM barrel) with endo-alpha-1,4-N-acetylgalactosaminidase activity, and a C-terminal deacetylase domain that founds carbohydrate esterase family CE21. After the GalNAc polymer crosses the inner membrane, PelA partially deacetylates and can hydrolyse it. PelA binds the periplasmic TPR domain of the outer-membrane porin PelB, which increases deacetylation and decreases hydrolysis before Pel is exported. Deacetylase active-site mutants make no Pel-reactive material and are defective in Pel-dependent biofilm formation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019213 deacetylase activity | IBA GO_REF:0000033 | MODIFY | Summary: IBA from PTN002441861, whose deacetylase IBD is seeded only by this gene's own PseudoCAP IDA row. The target in its own WITH/FROM is expected. Reason: Correct for PelA but general. PelA deacetylates GalNAc residues of Pel and of alpha-1,4-GalNAc oligosaccharides, so the specific child N-acetylgalactosaminoglycan deacetylase activity is supported. Separately, the node is a poor place for this term: its other two leaves contain only the GH114-like hydrolase domain and lack the CE21 deacetylase domain (see source defect). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002441861 SUPPORTS TRANSFER Sound for PelA itself (its own IDA seeds the node); refine to the GalNAc-polymer deacetylase. The node also covers leaves lacking the deacetylase domain, which is a problem for those leaves, not this one. Proposed replacements: N-acetylgalactosaminoglycan deacetylase activity Supporting Evidence: PMID:40120681 After synthesis and transport of the GalNAc polysaccharide across the inner membrane, PelA partially deacetylates and hydrolyzes Pel before its export out of the cell via PelB. PMID:40120681 Importantly, we show using MALDI-TOF MS that the interaction of PaPelA with PaPelB results in increased deacetylation of Ξ±-1,4-GalNAc oligosaccharides (Fig. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro glycoside hydrolase/deacetylase beta/alpha-barrel mapping. Reason: True but uninformative. PelA modifies the Pel polysaccharide during its synthesis and export, so the specific process is polysaccharide biosynthetic process, which the gene already carries (TAS). Proposed replacements: polysaccharide biosynthetic process Supporting Evidence: PMID:23504011 Finally, antiserum against the Pel polysaccharide was generated, and PelA deacetylase mutants do not produce Pel-reactive material. |
| GO:0000271 polysaccharide biosynthetic process | TAS PMID:28715477 The RhlR quorum-sensing receptor controls Pseudomonas aerugi... | ACCEPT | Summary: PHI-base TAS from a RhlR quorum-sensing paper that used a pelA deletion to test Pel-dependence of colony biofilms. Reason: The claim is correct: PelA deacetylase activity is required for Pel production, and PelA modifies the polymer before export. The cited paper is a weak source (it uses a pelA mutant as a tool), but the primary literature supports the claim. GO has no Pel-specific biosynthesis term. Supporting Evidence: PMID:23504011 Taken together, these results suggest that the deacetylase activity of PelA is important for the production of the Pel polysaccharide. PMID:28715477 We examined the colony biofilm phenotypes of the ΞpelA single and the ΞrhlRΞpelA and ΞrhlIΞpelA double mutants. |
| GO:0019213 deacetylase activity | IDA PMID:23504011 PelA deacetylase activity is required for Pel polysaccharide... | MODIFY | Summary: PseudoCAP IDA; sole seed of the PTN002441861 deacetylase activity IBD. Purified recombinant PelA hydrolysed p-nitrophenyl acetate, and predicted active-site mutants lost more than 90% of activity. Reason: The seed is sound: a direct assay of the purified protein with active-site mutants. The pseudosubstrate supports only generic deacetylase activity, but later work shows deacetylation of alpha-1,4-GalNAc oligosaccharides, so the specific child term is now warranted, consistent with the IBA row. Proposed replacements: N-acetylgalactosaminoglycan deacetylase activity Supporting Evidence: PMID:23504011 We first established that purified recombinant PelA hydrolyzed the pseudosubstrate p -nitrophenyl acetate in vitro , and site-specific mutations of predicted deacetylase active-site residues reduced activity greater than 10-fold. PMID:40120681 Characterization of the deacetylase domain revealed that PelA is the founding member of a new carbohydrate esterase family, CE21. |
| GO:0044010 single-species biofilm formation | IMP PMID:23504011 PelA deacetylase activity is required for Pel polysaccharide... | KEEP AS NON CORE | Summary: PseudoCAP IMP. pelA deletion and deacetylase point mutants form reduced biofilms and lack wrinkly colony morphology. Reason: Correct mutant evidence. Biofilm formation is the downstream outcome of Pel production, which PelA performs by modifying the polymer, so the term is peripheral to its core enzymatic role. Supporting Evidence: PMID:23504011 PA14Ξ pelA formed significantly reduced biofilms compared to the parental strain and, likewise, each point mutant was comparably impaired ( Fig. |
| GO:0042597 periplasmic space | IDA PMID:23504011 PelA deacetylase activity is required for Pel polysaccharide... | NEW | Summary: Proposed. Subcellular fractionation with compartment controls placed PelA in periplasmic and membrane fractions, not cytoplasm. Reason: Two independent lines agree: fractionation with periplasmic (Bla), membrane (PelC) and cytoplasmic controls, and direct binding to the periplasmic TPR domain of PelB. PelA's substrate is the Pel polymer after it has crossed the inner membrane. Supporting Evidence: PMID:23504011 We found that PelA localized to both the periplasmic and membrane fractions but not to the cytoplasm. PMID:28972168 Combined, our results indicate that the TPR-containing domain of PelB localizes PelA to the PEL secretion apparatus within the periplasm |
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Download this section (compressed HTML)Q: Should GO add a term for endo-hydrolysis of alpha-1,4-linked N-acetylgalactosamine polymers (PelA GH166 activity)? GO:0033931 endogalactosaminidase activity is defined for deacetylated poly-galactosamine.
Q: Should the PTN002441861 deacetylase IBD be moved to a node restricted to PelA orthologs that contain the CE21 deacetylase domain?
Experiment: Express Dictyoglomus B8DZ50 and Deinococcus Q9RWG2 and test esterase activity on p-nitrophenyl acetate and alpha-1,4-GalNAc oligosaccharides alongside PelA, to confirm that they lack deacetylase activity.
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