PokMT1 from the Polyketomycin Biosynthetic Machinery of <i>Streptomyces diastatochromogenes</i> Tü6028 Belongs to the Emerging Family of <i>C</i>-Methyltransferases That Act on CoA-Activated Aromatic Substrates
Bibliographic record
Abstract
Recent biochemical characterizations of the MdpB2 CoA ligase and MdpB1 C -methyltransferase ( C -MT) from the maduropeptin (MDP, 2 ) biosynthetic machinery revealed unusual pathway logic involving C-methylation occurring on a CoA-activated aromatic substrate. Here we confirmed this pathway logic for the biosynthesis of polyketomycin (POK, 3 ). Biochemical characterization unambiguously established that PokM3 and PokMT1 catalyze the sequential conversion of 6-methylsalicylic acid (6-MSA, 4 ) to form 3,6-dimethylsalicylyl-CoA (3,6-DMSA-CoA, 6 ), which serves as the direct precursor for the 3,6-dimethylsalicylic acid (3,6-DMSA) moiety in the biosynthesis of 3 . PokMT1 catalyzes the C-methylation of 6-methylsalicylyl-CoA (6-MSA-CoA, 5 ) with a k cat of 1.9 min –1 and a K m of 2.2 ± 0.1 μM, representing the most proficient C -MT characterized to date. Bioinformatics analysis of MTs from natural product biosynthetic machineries demonstrated that PokMT1 and MdpB1 belong to a phylogenetic clade of C -MTs that preferably act on aromatic acids. Significantly, this clade includes the structurally characterized enzyme SibL, which catalyzes C-methylation of 3-hydroxykynurenine in its free acid form, using two conserved tyrosine residues for catalysis. A homology model and site-directed mutagenesis suggested that PokMT1 also employs this unusual arrangement of tyrosine residues to coordinate C-methylation but revealed a large cavity capable of accommodating the CoA moiety tethered to 5 . CoA activation of the aromatic acid substrate may represent a general strategy that could be exploited to improve catalytic efficiency. This study sets the stage to further investigate and exploit the catalytic utility of this emerging family of C -MTs in biocatalysis and synthetic biology.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".