| Claim/Topic | Key finding | Organism/system | Quantitative details | Source (authors, year, journal) | URL | Evidence citation id |
|---|---|---|---|---|---|---|
| Identity verification of target gene | trpB is explicitly annotated as PP_0083, tryptophan synthase beta subunit, in *Pseudomonas putida* KT2440, matching UniProt Q88RP6. | *P. putida* KT2440 | PP_0083 locus tag | Kim et al., 2013, *FEMS Microbiology Letters* | https://doi.org/10.1111/1574-6968.12135 | (pqac-00000008) |
| Operon organization | trpA and trpB are adjacent, overlap by 1 nucleotide, and are consistent with co-transcription as a trpBA operon. | *P. putida* KT2440 | 1-nt overlap between trpA and trpB | Molina-Henares et al., 2009, *Microbial Biotechnology* | https://doi.org/10.1111/j.1751-7915.2008.00062.x | (pqac-00000012) |
| Experimental operon confirmation | RT-PCR across the trpA/trpB region confirmed in vivo co-transcription of trpA and trpB. | *P. putida* KT2440 | cDNA band detected with A-1/B-1 primers; negative control lacked RT | Molina-Henares et al., 2009, *Microbial Biotechnology* | https://doi.org/10.1111/j.1751-7915.2008.00062.x | (pqac-00000013, pqac-00000015) |
| Broader pathway organization | Tryptophan biosynthesis genes are split across unlinked regions: trpBA cluster, trpGDC operon, and monocistronic trpE/trpF; trpI is divergently transcribed from trpBA. | *P. putida* KT2440 | Genomic organization into 2 clusters + 2 monocistronic units | Molina-Henares et al., 2009, *Microbial Biotechnology* | https://doi.org/10.1111/j.1751-7915.2008.00062.x | (pqac-00000013, pqac-00000016) |
| Genetic evidence for pathway function | Disruption of trpA causes tryptophan auxotrophy, supporting that the trpBA unit is required for de novo tryptophan synthesis. | *P. putida* KT2440 | Aux-1 insertion at 7th codon of trpA; TrpA mutant grows only with tryptophan supplementation | Molina-Henares et al., 2009, *Microbial Biotechnology* | https://doi.org/10.1111/j.1751-7915.2008.00062.x | (pqac-00000012, pqac-00000013, pqac-00000016) |
| trpI-associated regulation | A trpIAB arrangement was identified; trpI is required for indole-responsive activation of the PP_RS00425 promoter system derived from KT2440. | *P. putida* KT2440 system tested in *E. coli* and *Cupriavidus necator* | Induction observed with 1 mM indole only when trpI was present | Matulis et al., 2022, *International Journal of Molecular Sciences* | https://doi.org/10.3390/ijms23094649 | (pqac-00000014) |
| Indole-responsive biosensor utility | The PpTrpI/PPP_RS00425 gene expression system was developed as an indole biosensor and showed strong, specific induction by indole. | KT2440-derived regulatory parts in heterologous hosts | Up to 639.6-fold induction; linear response ~0.4-5 mM indole | Matulis et al., 2022, *International Journal of Molecular Sciences* | https://doi.org/10.3390/ijms23094649 | (pqac-00000014) |
| Indole stress response | trpB (PP_0083) was the most highly induced gene in KT2440 after indole treatment, linking it to indole-responsive physiology and tryptophan biosynthesis. | *P. putida* KT2440 | 3.52-fold upregulation; 47 genes changed >1.5-fold up or <0.67-fold down | Kim et al., 2013, *FEMS Microbiology Letters* | https://doi.org/10.1111/1574-6968.12135 | (pqac-00000008, pqac-00000009) |
| Functional interpretation of indole response | Authors proposed that degradation/incorporation of indole into tryptophan biosynthesis may help mitigate indole stress. | *P. putida* KT2440 | Qualitative interpretation from microarray data | Kim et al., 2013, *FEMS Microbiology Letters* | https://doi.org/10.1111/1574-6968.12135 | (pqac-00000009) |
| Core enzymatic reaction | TrpB catalyzes the PLP-dependent β-reaction converting indole + L-serine to L-tryptophan, the terminal step of tryptophan biosynthesis. | Bacterial tryptophan synthase | Reaction: indole + L-Ser → L-Trp + H2O | Ghosh et al., 2022, *Frontiers in Molecular Biosciences* | https://doi.org/10.3389/fmolb.2022.923042 | (pqac-00000000) |
| Catalytic intermediate and cofactor chemistry | TrpB forms a PLP-linked aminoacrylate (EAA) Schiff-base intermediate; PLP is present as an internal aldimine with a catalytic Lys. | Bacterial tryptophan synthase | Catalytic Lys87 noted in *Salmonella* numbering | Ghosh et al., 2022, *Frontiers in Molecular Biosciences*; Michalska et al., 2019, *IUCrJ* | https://doi.org/10.3389/fmolb.2022.923042 ; https://doi.org/10.1107/S2052252519005955 | (pqac-00000000, pqac-00000002) |
| Quaternary structure and channeling | TrpB usually functions in an α2β2 tryptophan synthase complex with TrpA; indole is channeled through an intersubunit tunnel. | Bacterial tryptophan synthase | ~25 Å tunnel connecting α and β active sites | Ghosh et al., 2022, *Frontiers in Molecular Biosciences*; Michalska et al., 2019, *IUCrJ* | https://doi.org/10.3389/fmolb.2022.923042 ; https://doi.org/10.1107/S2052252519005955 | (pqac-00000000, pqac-00000002) |
| Allosteric control and structure | TrpB contains an N-terminal COMM domain that participates in open/closed transitions and α-β allosteric communication. | Bacterial tryptophan synthase | Open (T) and closed (R) conformational states regulate catalysis | Ghosh et al., 2022, *Frontiers in Molecular Biosciences*; Michalska et al., 2019, *IUCrJ* | https://doi.org/10.3389/fmolb.2022.923042 ; https://doi.org/10.1107/S2052252519005955 | (pqac-00000000, pqac-00000002) |
| Structural conservation | Bacterial TrpB proteins are broadly conserved in fold and mechanism, supporting annotation transfer across species when identity is verified. | Multiple bacterial pathogens / bacterial TrpAB enzymes | TrpB described as more sequence- and fold-conserved than TrpA | Michalska et al., 2019, *IUCrJ*; Michalska et al., 2021, *Protein Science* | https://doi.org/10.1107/S2052252519005955 ; https://doi.org/10.1002/pro.4143 | (pqac-00000002, pqac-00000006) |
| 2024 mechanistic advance | A single substitution at the near-universally conserved catalytic glutamate can unlock latent tyrosine synthase activity in TrpB. | Engineered TrpB (Tm9D8* lineage) | E105G gave 18-fold activation on 1-naphthol and >100-fold on phenol in one context | Almhjell et al., 2024, *Nature Chemical Biology* | https://doi.org/10.1038/s41589-024-01619-z | (pqac-00000017, pqac-00000018) |
| 2024 evolved activity gains | Directed evolution converted TrpB into TyrS variants with very large activity gains and exclusive para-selective C-C bond formation on phenols. | Engineered TrpB/TyrS | >30,000-fold overall rate enhancement; ≥99.5% enantio- and regioselectivity | Almhjell et al., 2024, *Nature Chemical Biology* | https://doi.org/10.1038/s41589-024-01619-z | (pqac-00000018, pqac-00000020) |
| 2024 catalytic performance | Final TyrS variant synthesized tyrosine with measurable catalytic turnover under preparative conditions. | Engineered TrpB/TyrS6 | Apparent TOF ~0.23 min⁻1 at 37 °C, 50 mM substrate | Almhjell et al., 2024, *Nature Chemical Biology* | https://doi.org/10.1038/s41589-024-01619-z | (pqac-00000017) |
| 2024 evolutionary/structural insight | The catalytic glutamate targeted in TyrS engineering is highly conserved across TrpB-like sequences, underscoring mechanistic importance. | TrpB-like sequence space | E105 conserved in ~98.3% of ~18,051 sequences | Almhjell et al., 2024, *Nature Chemical Biology* | https://doi.org/10.1038/s41589-024-01619-z | (pqac-00000018, pqac-00000019) |
| 2024 practical application | Engineered TyrS enzymes enabled preparative/gram-scale synthesis of tyrosine analogs. | Engineered TrpB/TyrS | Preparative scale; multi-gram / gram-scale products reported | Almhjell et al., 2024, *Nature Chemical Biology* | https://doi.org/10.1038/s41589-024-01619-z | (pqac-00000019, pqac-00000020) |
| Stand-alone TrpB biocatalyst engineering | Directed evolution liberated TrpB from dependence on TrpA, creating stand-alone catalysts suitable for synthesis of noncanonical amino acids. | Engineered PfTrpB / TmTrpB variants | PfTrpB0B2 obtained with 6 mutations after 3 rounds; 83-fold increase in catalytic efficiency | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000025) |
| Substrate scope and yields | Evolved TrpB variants accept many substituted indoles and often give high isolated yields. | Engineered TrpB biocatalysts | Typical isolated yields 70-99% across many analogs | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000025) |
| Preparative Trp analog synthesis | A TmTrpB variant was used to synthesize 4-cyanotryptophan on preparative scale. | Engineered TmTrpB9D8* in *E. coli* cells | 800 mg 4-cyanoTrp from 1 L culture; 49% yield | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000025) |
| Expanded bond-forming chemistry | Engineered TrpB variants catalyze noncanonical C-C, C-N, C-S, and C-Se bond-forming reactions. | Engineered TrpB biocatalysts | Up to 2,700 turnovers on nitro-containing substrates | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000023, pqac-00000024) |
| Quaternary-center synthesis | Engineered PfTrpBquat shifted chemoselectivity to C3 alkylation of oxindoles, enabling quaternary stereocenter formation. | Engineered PfTrpBquat | >99% C3 chemoselectivity; 52% yield; 122 mg from 1 mmol substrate using 100 mL *E. coli* culture | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000023) |
| Azulene amino acid production | Evolution improved azulene alkylation and enabled gram-scale synthesis of AzAla. | Engineered TmTrpBAzul | Activity improved from 4.6 to 14.0 turnovers/min; 965 mg product; 57% isolated yield | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000023, pqac-00000026) |
| β-branched amino acid synthesis | TrpB engineering enabled efficient β-methyltryptophan synthesis from threonine-derived chemistry. | Engineered PfTrpB variants | >6,000-fold boost in β-methylTrp activity vs WT; one variant used 1 equiv Thr and gave 3.5-fold higher yield than prior variant needing 10 equiv | Watkins-Dulaney et al., 2021, *ChemBioChem* | https://doi.org/10.1002/cbic.202000379 | (pqac-00000024) |


*Table: This table compiles organism-specific evidence for *Pseudomonas putida* KT2440 trpB (PP_0083; UniProt Q88RP6) together with conserved TrpB mechanistic knowledge and recent engineering/application advances. It is useful for separating direct evidence about the target gene from broader, high-confidence functional inference about TrpB enzymes.*