CatB is the cytosolic Mn(2+)-dependent muconate cycloisomerase of the catechol ortho-cleavage branch of aromatic compound catabolism in Pseudomonas putida KT2440. It catalyzes the reversible conversion of cis,cis-muconate to (+)-muconolactone downstream of catechol 1,2-dioxygenase and functions in the CatR-regulated catBCA module of the beta-ketoadipate pathway.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: CatB is an enzyme, so catalytic activity is technically correct, but this annotation is too generic to be informative. The specific molecular function is already captured by muconate cycloisomerase activity (GO:0018849), which precisely reflects the reaction catalyzed by PP_3715. Reason: A highly specific catalytic term is already present, making the generic parent term redundant. |
| GO:0006518 peptide metabolic process | IEA GO_REF:0000117 | REMOVE | Summary: This annotation is not supported for catB. The literature consistently places catB in benzoate/catechol degradation and the beta-ketoadipate pathway, with no evidence for a role in peptide metabolism. This appears to be erroneous automated transfer from a broad mandelate racemase/muconate lactonizing family rather than from the specific function of PP_3715. Reason: CatB is a muconate cycloisomerase in aromatic compound catabolism, not a peptide metabolic enzyme. Supporting Evidence: PMID:2449420 The catB and catC genes encode cis,cis-muconate lactonizing enzyme I (EC 5.5.1.1) and muconolactone isomerase (EC 5.3.3.4), respectively. These enzymes are required for the dissimilation of benzoate to beta-ketoadipate by Pseudomonas putida... PMID:3609743 The enzyme, cis,cis-muconate lactonizing enzyme I (MLEI; EC 5.5.1.1), has been proposed to play a key role in the beta-ketoadipate pathway of benzoate degradation. |
| GO:0009063 amino acid catabolic process | IEA GO_REF:0000002 | REMOVE | Summary: This process annotation is inconsistent with the experimentally supported role of catB in aromatic compound degradation. Although the broader enzyme superfamily contains proteins involved in other chemistries, PP_3715 is specifically the cis,cis-muconate lactonizing enzyme of benzoate/catechol catabolism in the beta-ketoadipate pathway. Reason: The annotation reflects family-level conflation rather than the specific biology of catB in P. putida KT2440. Supporting Evidence: PMID:2449420 The catB and catC genes encode cis,cis-muconate lactonizing enzyme I (EC 5.5.1.1) and muconolactone isomerase (EC 5.3.3.4), respectively. These enzymes are required for the dissimilation of benzoate to beta-ketoadipate by Pseudomonas putida... file:PSEPK/catB/catB-deep-research-falcon.md The **Ξ²-ketoadipate pathway** is a central aerobic aromatic catabolic route. In KT2440, aromatic compounds such as benzoate can be converted to catechol, which is cleaved by **catechol 1,2-dioxygenase (CatA)** to form **cis,cis-muconate**; this intermediate is then processed by CatB and CatC and ultimately funneled toward central metabolism |
| GO:0018849 muconate cycloisomerase activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the precise core molecular function of CatB. Classical biochemical work in P. putida showed that cis,cis-muconate cycloisomerase catalyzes the reversible interconversion of cis,cis-muconate and (+)-muconolactone, and the cloned catB gene was identified as encoding cis,cis-muconate lactonizing enzyme I (EC 5.5.1.1). Reason: GO:0018849 accurately captures the specific enzymatic reaction catalyzed by PP_3715 and represents the core molecular activity of the gene. Supporting Evidence: PMID:6652062 Steady-state kinetic analysis of the divalent metal ion requiring cis,cis-muconate cycloisomerase catalyzed interconversion of cis,cis-muconate and (+)-muconolactone... PMID:3609743 The enzyme, cis,cis-muconate lactonizing enzyme I (MLEI; EC 5.5.1.1), has been proposed to play a key role in the beta-ketoadipate pathway of benzoate degradation. |
| GO:0018850 chloromuconate cycloisomerase activity | IEA GO_REF:0000002 | REMOVE | Summary: This annotation is not supported for wild-type P. putida CatB. The shared InterPro family includes both muconate and chloromuconate cycloisomerases, but substrate-specificity experiments showed that the P. putida muconate cycloisomerase does not appreciably transform the chlorinated muconates characteristic of chloromuconate cycloisomerases. The automated annotation therefore overextends a family assignment into a distinct catalytic specialization. Reason: The evidence supports muconate cycloisomerase activity, not the chloromuconate-specific/dehalogenating activity of chlorocatechol pathways. Supporting Evidence: PMID:9726873 We show that they transform, in addition to cis,cis-muconate, 3-fluoro-, 2-methyl-, and 3-methyl-cis, cis-muconate with high specificity constants but not 2-fluoro-, 2-chloro-, 3-chloro-, or 2,4-dichloro-cis,cis-muconate. |
| GO:0030145 manganese ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: This annotation is supported by biochemical characterization of the P. putida enzyme. cis,cis-Muconate cycloisomerase is a divalent-metal dependent enzyme, and Mn(2+) titration experiments identified a single manganous-ion binding site per subunit. Manganese binding is therefore a real and mechanistically relevant feature of CatB rather than a generic metal-association prediction. Reason: Mn(2+) binding is directly connected to catalytic function and is experimentally supported for the P. putida enzyme. Supporting Evidence: PMID:6652062 The titration of enzyme freed of divalent metal ion with manganous ion, monitored by electron paramagnetic resonance spectroscopy and steady-state kinetic measurements, indicates a single binding site per subunit... |
| GO:0042952 beta-ketoadipate pathway | IEA file:PSEPK/catB/catB-deep-research-falcon.md | NEW | Summary: catB should also be represented at the biological-process level as part of the beta-ketoadipate pathway. catB and catC were originally described as enzymes required for the dissimilation of benzoate to beta-ketoadipate in P. putida, and the Falcon synthesis places CatB in the catechol ortho-cleavage branch that channels aromatic substrates into central metabolism. Supporting Evidence: PMID:2449420 The catB and catC genes encode cis,cis-muconate lactonizing enzyme I (EC 5.5.1.1) and muconolactone isomerase (EC 5.3.3.4), respectively. These enzymes are required for the dissimilation of benzoate to beta-ketoadipate by Pseudomonas putida... file:PSEPK/catB/catB-deep-research-falcon.md CatB is a central enzyme in the **catechol ortho-cleavage / Ξ²-ketoadipate pathway**, converting ring-cleavage product muconate toward central metabolism. |
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Download this section (compressed HTML)Q: What sequence determinants distinguish KT2440 CatB from true chloromuconate cycloisomerases despite their shared InterPro assignment?
Suggested experts: aromatic-catabolism enzymologists, structure-function specialists in the mandelate racemase/muconate lactonizing family
Q: Under which aromatic substrates or stress conditions does catB become a major flux-control point relative to catA, catC, and parallel catechol-entry reactions in KT2440?
Suggested experts: Pseudomonas metabolism researchers, systems biologists studying aromatic funneling
Experiment: Purify PP_3715 from KT2440 and compare turnover of cis,cis-muconate versus chlorinated muconate analogs to directly test and retire the chloromuconate activity inference.
Type: substrate-specificity biochemistry
Experiment: Quantify growth, muconate accumulation, and catB expression in wild-type and catR-perturbed KT2440 on benzoate, catechol, phenol, and chlorobenzoate-related substrates to define the operational pathway scope of CatB.
Type: pathway-flux analysis
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