What this entity is
The beta-ketoadipate pathway is an aromatic-compound degradation pathway examined as part of the FBA–experimental growth comparison in Acinetobacter baylyi ADP1. 1
Canonical name: beta-ketoadipate pathway. 1
Known aliases: none reported in the source. 1
Stable external identifier: none reported in the source. 1
It is related to aromatic amino acid biosynthesis, quinate-degradation-pathway, metabolic-model-gapfilling, and flux-balance-analysis. 1
The pathway is the central route in a 51-gene quinate-catabolism support network, converting quinate through protocatechuate and beta-ketoadipate to succinyl-CoA and acetyl-CoA for entry into the TCA cycle. 2 The network identifies respiratory, iron-acquisition, PQQ-cofactor, and regulatory functions as metabolic support for the pathway, refining its interpretation from an isolated degradation route to a distributed dependency system. 2
The respiratory-chain analysis further refines this interpretation: quinate catabolism theoretically produces 4 NADH, or 0.57 NADH per carbon, and generates succinyl-CoA and acetyl-CoA simultaneously through aromatic-ring cleavage, potentially creating a concentrated TCA-cycle NADH burst. 3 This supports a hypothesis that the pathway’s respiratory requirement reflects NADH flux rate and dehydrogenase capacity, rather than total reducing-equivalent yield alone; the proposed flux pattern is based on theoretical stoichiometry, not measured flux distributions. 3
Evidence from adp1_triple_essentiality
Aromatic degradation was strongly enriched among genes discordant between FBA predictions and experimental phenotypes: 9 of 11 genes were discordant, with odds ratio (OR) = 9.70 and Benjamini-Hochberg false discovery rate (FDR)-adjusted q = 0.012. 1
Directional enrichment for FBA under-prediction was also observed for aromatic degradation, with OR = 12.0 and FDR-adjusted q = 0.004. 1
The report identifies beta-ketoadipate-pathway genes, including 4-carboxymuconolactone decarboxylase and beta-ketoadipate enol-lactone hydrolase, as examples of genes predicted as blocked by FBA but associated with experimental growth defects. 1
These observations support the hypothesis that missing aromatic substrates or mismatched environmental assumptions, rather than network topology alone, may explain part of the pathway’s FBA–growth discordance. 1 The new network analysis supports this model-gap interpretation: FBA captures a 1.76× higher Complex I flux on aromatic substrates than on the comparison condition, with fluxes of 0.55 versus 0.31, yet predicts 0% essentiality for Complex I. 2 The respiratory-chain analysis further supports the model-gap interpretation by showing that FBA routes NADH through Complex I and predicts zero flux through alternative dehydrogenases, potentially missing capacity-limited, condition-specific respiratory requirements. 3 The proposed explanation that trace aromatic compounds in experimental media account for the discordance remains untested and requires measured media composition together with revised FBA constraints. 1
Related evidence
Quinate dehydrogenase requires the PQQ cofactor, while protocatechuate 3,4-dioxygenase requires non-heme Fe²⁺ for ring cleavage, linking pathway activity to cofactor supply and iron acquisition. 2 The 51-gene network assigns 8 genes to aromatic functions, 21 to Complex I, 7 to iron acquisition, and 2 to PQQ biosynthesis; 30/51 genes lack FBA reaction mappings, refining the earlier evidence for model under-representation of pathway-support functions. 2
Condition-specific FBA flux showed weak and mixed correlations with measured growth across tested carbon sources, including glucarate ρ = +0.246 (p = 0.005; n = 127), a positive correlation opposite to the expected direction. 1
The PQQ dependency supports aromatic-catabolism involvement but is not exclusive to it: PQQ-biosynthesis genes also appear as glucose-specific in the deletion-phenotype analysis, where they are associated with PQQ-dependent glucose dehydrogenase. 2 The respiratory-chain report adds that Complex I has a growth ratio of 0.37 on quinate, compared with 1.44 on glucose, supporting a qualitative, substrate-specific respiratory requirement associated with quinate catabolism rather than a simple dependence on total NADH yield. 3 This entity therefore contributes to gene-essentiality, condition-specific-fitness, metabolic-model-gapfilling, and multi-omics-integration through model–phenotype comparison and integrated pathway-support evidence. 1,2
Open directions
- Add trace aromatic compounds to the FBA media definitions and test whether predictions for the implicated beta-ketoadipate-pathway genes improve. 1
- Measure experimental media composition and compare it with condition-specific FBA constraints to test whether environmental assumptions explain the discordance. 1
- Add PQQ biosynthesis, iron homeostasis, and respiratory-chain capacity constraints to the ADP1 FBA model and test whether pathway-support essentiality is better captured. 2
- Perform condition-matched knockout and TnSeq experiments for the implicated pathway genes to determine whether their growth defects are reproducible under the relevant aromatic conditions. 1
- Measure NADH/NAD⁺ ratios and respiratory-chain protein abundance during quinate versus succinate growth, and test whether the predicted concentrated NADH burst explains the quinate-specific Complex I requirement. 3
See the source summaries: Triple Essentiality Concordance Analysis for *Acinetobacter baylyi* ADP1, Aromatic Catabolism Support Network in ADP1, and Condition-Specific Respiratory Chain Wiring in ADP1.