| Aspect | Specific claim for Q88HK0/Fcs | Evidence type | Key sources with year + URL |
|---|---|---|---|
| Gene/protein identity | In *Pseudomonas putida* KT2440, **fcs = PP_3356** and encodes the feruloyl-CoA synthetase in the ferulate/coumarate catabolic branch; this matches UniProt Q88HK0. | Pathway mapping; gene annotation in primary literature | García-Hidalgo et al., 2020, https://doi.org/10.1128/AEM.02442-19 (pqac-00000008, pqac-00000014) |
| Enzyme class / family | Fcs is an **acid-thiol ligase / acyl-CoA synthetase** of the **ANL/AMP-binding** enzyme superfamily; UniProt domain architecture (AMP-binding / ANL_N) is consistent with this class. | Curated database annotation + review synthesis | UniProt Q88HK0 (provided by user); Tramontina et al., 2023, https://doi.org/10.1007/s00253-023-12571-8 (pqac-00000015) |
| Reaction description | Fcs catalyzes the **ATP-dependent CoA thioesterification** of hydroxycinnamates, especially **ferulate** and **p-coumarate**, yielding the corresponding CoA esters (feruloyl-CoA or coumaroyl-CoA) as the activation step for downstream catabolism. | Review synthesis + in vivo product detection | Tramontina et al., 2023, https://doi.org/10.1007/s00253-023-12571-8 (pqac-00000015); Incha et al., 2020, https://doi.org/10.1016/j.mec.2019.e00119 (pqac-00000007); Incha, 2023, coumaroyl-CoA LC-MS/MS detection (pqac-00000011, pqac-00000012) |
| Substrate scope | For KT2440, literature supports activity in catabolism of both **ferulate** and **p-coumarate**; broader FCS homolog literature supports hydroxycinnamate activation more generally, including caffeate/sinapate in related enzymes, but that broader scope is not directly proven here for Q88HK0. | Direct organism-specific pathway evidence + homolog biochemical inference | García-Hidalgo et al., 2020, https://doi.org/10.1128/AEM.02442-19 (pqac-00000008, pqac-00000014); Tramontina et al., 2023, https://doi.org/10.1007/s00253-023-12571-8 (pqac-00000015); Gonçalves et al., 2022, https://doi.org/10.1007/s00253-022-11885-3 (pqac-00000017, pqac-00000019) |
| Pathway position | Fcs is the **entry activation step** in the hydroxycinnamate funnel: **ferulate / p-coumarate → feruloyl-/coumaroyl-CoA → vanillin / 4-hydroxybenzaldehyde → vanillic / 4-hydroxybenzoic acid → protocatechuate → β-ketoadipate pathway**. | Pathway diagrams; systems biology; reviews | García-Hidalgo et al., 2020, https://doi.org/10.1128/AEM.02442-19 (pqac-00000014); Ruhl et al., 2025, https://doi.org/10.1111/1751-7915.70152 (pqac-00000002, pqac-00000013); Zhou et al., 2025 preprint, https://doi.org/10.1101/2025.03.24.645021 (pqac-00000003) |
| Genomic neighborhood | The pathway map places **fcs (PP_3356)** adjacent to **vdh (PP_3357)** and **PP_3358** (the enzyme converting CoA-thioesters toward aromatic aldehydes), supporting a local ferulate catabolic gene neighborhood. | Genomic pathway mapping | García-Hidalgo et al., 2020, https://doi.org/10.1128/AEM.02442-19 (pqac-00000008, pqac-00000014) |
| Regulation | The global carbon catabolite repression regulator **Crc** likely represses **fcs, ech, and vdh**; deleting **crc** accelerated ferulate and p-coumarate utilization, consistent with **derepression** of this branch. | Genetic perturbation / regulatory inference in engineered strains | Werner et al., 2023, https://doi.org/10.1126/sciadv.adj0053 (pqac-00000009) |
| Functional module evidence | Machine-learning analysis of RB-TnSeq fitness data grouped **Fcs:Ech:Vdh** into a hydroxycinnamate catabolism module (**fModule_14**), linking this branch to **acetyl-CoA production** and glyoxylate-shunt dependence. | Functional genomics + machine learning + mutant validation | Borchert et al., 2024, https://doi.org/10.1128/msystems.00942-23 (pqac-00000025, pqac-00000028) |
| Localization | The best-supported interpretation is that Fcs is **primarily intracellular/cell-associated** because its CoA-ester products were measured from intracellular extracts; however, aromatic-catabolic enzymes as a class can appear in **outer membrane vesicles (OMVs)** during lignin growth, and β-ketoadipate-pathway proteins are OMV-enriched, so extracellular packaging of some pathway enzymes is possible. **Direct OMV-specific evidence for Fcs itself remains uncertain in the retrieved text.** | Intracellular metabolite extraction; OMV proteomics; cautious inference | Incha, 2023 (intracellular CoA-esters), (pqac-00000023); Salvachúa et al., 2020, https://doi.org/10.1073/pnas.1921073117 (pqac-00000020, pqac-00000021, pqac-00000022, pqac-00000024) |
| Phenotype / toxicity | Overexpression or increased flux through Fcs in the presence of coumarate causes **coumaroyl-CoA accumulation** and **growth inhibition / lag**, indicating the activated CoA-thioester can be toxic when downstream consumption is limiting. | In vivo metabolic engineering phenotype + metabolite measurement | Incha et al., 2020, https://doi.org/10.1016/j.mec.2019.e00119 (pqac-00000007); Incha, 2023 (pqac-00000006, pqac-00000011, pqac-00000026) |
| Engineering relevance | Fcs is repeatedly leveraged for **lignin-derived aromatic valorization**: vanillin accumulation from ferulate, β-ketoadipate production from lignin monomers, and precursor supply for non-native products such as bisdemethoxycurcumin. | Metabolic engineering and bioprocess studies | Werner et al., 2023, https://doi.org/10.1126/sciadv.adj0053 (pqac-00000009); Jin et al., 2024, https://doi.org/10.3390/molecules29071555 (pqac-00000010); Incha et al., 2020, https://doi.org/10.1016/j.mec.2019.e00119 (pqac-00000007); Ruhl et al., 2025, https://doi.org/10.1111/1751-7915.70152 (pqac-00000013) |
| Quantitative application notes | Recent pathway-centered applications report: **β-ketoadipate up to 44.5 ± 1.85 g/L** and **0.85 ± 0.04 g/L/h** from lignin-related aromatics after pathway/regulatory engineering; engineered KT2440 also accumulated **0.64 g/L vanillin**, increased to **3.35 g/L apparent total recovery** with in situ resin recovery. | Bioprocess performance data | Werner et al., 2023, https://doi.org/10.1126/sciadv.adj0053 (pqac-00000009); Ruhl et al., 2025, https://doi.org/10.1111/1751-7915.70152 (pqac-00000013) |


*Table: This table summarizes the functional annotation of Pseudomonas putida KT2440 fcs (PP_3356; UniProt Q88HK0), including its enzymatic role, pathway placement, regulation, localization, and engineering relevance. It is useful as a compact evidence map linking gene identity to experimentally supported function and recent applications.*