| Focus | Main finding about PqqE or pqq locus | Key quantitative/statistical details (if any) | Publication (authors, journal, year, month/day if available) | URL/DOI |
|---|---|---|---|---|
| Identity / catalytic role | In *Methylorubrum extorquens* AM1, PqqE is the radical SAM enzyme that initiates PQQ biosynthesis by forming the first C–C crosslink in the peptide precursor PqqA, coupling Glu and Tyr side chains; activity requires the peptide chaperone PqqD. (pqac-00000000, pqac-00000001, pqac-00000007) | Deuterium-labeling showed transfer of deuterium from Glu β-position into 5'-deoxyadenosyl product, supporting H-abstraction by 5'-dAdo radical; reaction is regioselective for Tyr ortho position. (pqac-00000000) | Yao & Morinaka, *Chemical Society Reviews*, 2026 Feb; citing mechanistic work in the field. (pqac-00000000) | https://doi.org/10.1039/d5cs00585j |
| Cofactors / domains | PqqE is a SPASM-domain radical SAM enzyme containing the canonical RS [4Fe–4S] cluster plus two auxiliary Fe–S clusters in the C-terminal SPASM domain; AuxII was observed as a [4Fe–4S] cluster coordinated by three Cys and Asp319, while AuxI appeared as [2Fe–2S] in the crystal. (pqac-00000000) | Two auxiliary clusters assigned; low-potential reductants were needed to access some redox states in spectroscopic studies. (pqac-00000000) | Yao & Morinaka, *Chemical Society Reviews*, 2026 Feb. (pqac-00000000) | https://doi.org/10.1039/d5cs00585j |
| Early pathway intermediate | PqqE/PqqD generate a crosslinked PqqA species (PqqA*), which is the early di-amino-acid precursor subsequently processed by downstream enzymes/proteases in the PQQ pathway. (pqac-00000003, pqac-00000005) | No enzyme kinetic constants reported in the provided excerpts. | Martins et al., *Journal of Biological Chemistry*, 2019 Oct. (pqac-00000003, pqac-00000005) | https://doi.org/10.1074/jbc.ra119.009684 |
| Genomic organization in AM1 | In *M. extorquens* AM1, pqq genes are split across at least two loci in genome-era analyses, with pqqABC/DE in the methylotrophy island and pqqFG separate; later work also depicts a local neighborhood including pqqE, pqqC/D, pqqB, pqqA, pqqF, and pqqG. (pqac-00000008, pqac-00000010, pqac-00000013) | PQQ biosynthesis module comprises 6 genes in one genomic overview, with pqqFG separate; another map shows multiple nearby pqqA annotations. (pqac-00000010, pqac-00000013) | Chistoserdova et al., *Journal of Bacteriology*, 2003 May; Martins et al., *Journal of Biological Chemistry*, 2019 Oct. (pqac-00000008, pqac-00000010, pqac-00000013) | https://doi.org/10.1128/jb.185.10.2980-2987.2003; https://doi.org/10.1074/jbc.ra119.009684 |
| Physiological context / localization | PQQ is produced for use as a redox cofactor by methanol dehydrogenases in methylotrophy; mature PQQ accumulates in the periplasmic space, whereas PqqE acts on the cytosolic ribosomal peptide precursor PqqA before downstream processing. (pqac-00000005, pqac-00000008, pqac-00000009) | No direct localization experiment for PqqE reported in provided excerpts; periplasmic accumulation is stated for mature PQQ. (pqac-00000005) | Chistoserdova et al., *Journal of Bacteriology*, 2003 May; Toyama, book chapter, 2016 Apr; Martins et al., *Journal of Biological Chemistry*, 2019 Oct. (pqac-00000005, pqac-00000008, pqac-00000009) | https://doi.org/10.1128/jb.185.10.2980-2987.2003; https://doi.org/10.1002/9783527681754.ch13; https://doi.org/10.1074/jbc.ra119.009684 |
| Organism-specific historical characterization | pqqE and pqqF were specifically sequenced/characterized in *Methylobacterium*/*Methylorubrum extorquens* AM1, supporting that the literature is about the same AM1 system as UniProt P71517. (pqac-00000011, pqac-00000014) | Historical sequencing/characterization noted; no quantitative values in excerpt. | Martins et al., *Journal of Biological Chemistry*, 2019 Oct; Ochsner et al., *Applied Microbiology and Biotechnology*, 2015 Nov. (pqac-00000011, pqac-00000014) | https://doi.org/10.1074/jbc.ra119.009684; https://doi.org/10.1007/s00253-014-6240-3 |
| Recent application: industrial PQQ production | Recent engineering of methylotrophs for PQQ overproduction links improved production to upregulation of PQQ biosynthesis genes, including strong induction of pqqE, showing practical value of the pathway. (pqac-00000015, pqac-00000016, pqac-00000019) | In *Hyphomicrobium denitrificans* FJNU-A26, pqqE expression increased ~6× vs wild type at later times; final titer reached 1.52 g/L, yield 40.3 mg/g DCW, productivity ~10.5 mg/L·h after 144 h fed-batch. (pqac-00000015, pqac-00000018) | Ren et al., *Biotechnology for Biofuels and Bioproducts*, 2023 Jan. (pqac-00000015, pqac-00000016, pqac-00000018, pqac-00000019) | https://doi.org/10.1186/s13068-023-02261-y |
| Recent application: phosphate-solubilization marker biology | Across 76 phosphate-solubilizing bacteria, the pqq cluster was treated as a genomic marker of PQQ-mediated glucose oxidation; the pathway description includes PqqE as the radical SAM enzyme in PQQ formation. (pqac-00000020, pqac-00000022, pqac-00000024) | Strong correlations reported between 2-keto-D-gluconic acid and pqq genes: 0.988–0.995 for pqqA–pqqE; P release vs pqqC correlation 0.940*; *P* < 0.05 or **P** < 0.01 as indicated. (pqac-00000020, pqac-00000021) | Chen et al., *AMB Express*, 2024 Jul. (pqac-00000020, pqac-00000021, pqac-00000022, pqac-00000024) | https://doi.org/10.1186/s13568-024-01745-w |


*Table: This table compiles the most relevant evidence-supported sources on PqqE in *Methylorubrum extorquens* AM1 and the broader PQQ biosynthetic pathway. It highlights identity verification, mechanism, gene organization, physiological context, and recent application-oriented studies with quantitative results where available.*