MJ1511 is a small (107 aa), uncharacterized protein from the hyperthermophilic archaeon Methanocaldococcus jannaschii. It belongs to the AhpD-like / CMD (carboxymuconolactone decarboxylase-like) structural superfamily (IPR029032, IPR003779, Pfam PF02627). However, MJ1511 lacks the conserved CXXC catalytic motif that is essential for canonical AhpD peroxidase activity. Its two cysteines (Cys-17 and Cys-107) are separated by 90 residues, unlike the 2-3 residue spacing seen in functionally characterized AhpD enzymes. No direct experimental literature exists for this protein. Its function remains genuinely uncertain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016491 oxidoreductase activity | IBA GO_REF:0000033 | REMOVE | Summary: IBA annotation for oxidoreductase activity based on PANTHER phylogenetic inference (PTN002142863) using M. tuberculosis AhpD (P9WQB5) as reference. The phylogenetic transfer is questionable because MJ1511 lacks the conserved CXXC catalytic motif that is essential for AhpD-type thiol-disulfide oxidoreductase activity. P9WQB5 has Cys-130/Cys-133 in a CXXC motif, while MJ1511 has only Cys-17 and Cys-107 separated by 90 residues. The AhpD-like fold is conserved, but the catalytic machinery for oxidoreductase activity appears absent. Reason: This IBA annotation is an over-propagated phylogenetic inference (from M. tuberculosis AhpD, P9WQB5, via PANTHER) that can be argued against on structural grounds, so it is removed. A dedicated 3-iteration OpenScientist structural investigation (AlphaFold + Foldseek) found that MJ1511 lacks every component of the AhpD catalytic machinery: no CXXC redox motif (its two cysteines, Cys17 and Cys107, sit 36.52 Angstroms apart in the AlphaFold model AF-Q58906-F1, mean pLDDT 93.8, versus the ~2 Angstrom spacing required for disulfide chemistry), zero histidine residues (so the catalytic Glu-His-water-Cys proton relay cannot form), and five alternative redox mechanisms were systematically excluded. The paralog MJ0742 (PDB 3D7I) carries the identical GO:0016491 (IBA) annotation despite the same missing catalytic residues, indicating a systematic mis-annotation of methanogen CMD proteins rather than a real function. MJ1511 is best classified as a CMD-family protein of unknown, likely pseudoenzyme, function. Supporting Evidence: PMID:11914371 The two catalytic sulfhydryl groups, Cys-130 and Cys-133, are located near a central cavity in the trimer PMID:12761216 The collective results strongly support the proposed catalytic mechanism for AhpD PMID:21615954 the functional activity is supplied by a proton relay system of five residues, Glu36, Cys48, Tyr50, Cys51, and His55, and one structural water molecule file:METJA/MJ1511/MJ1511-deep-research-bioreason-sft.md [BioReason SFT trace identifies AhpD-like fold but functional claims are largely unsupported] file:METJA/MJ1511/MJ1511-hypotheses/pseudoenzyme-cxxc-loss/openscientist.md MJ1511 is best classified as a CMD-family protein of unknown function, consistent with pseudoenzyme status. file:METJA/MJ1511/MJ1511-hypotheses/pseudoenzyme-cxxc-loss/openscientist.md The paralog MJ0742 (PDB 3D7I, 1.75 Angstrom crystal structure) shares the same pattern of missing catalytic residues (1 Cys, 0 His, no CXXC) and the same erroneous GO annotations, reinforcing that this is a systematic annotation error affecting methanogen CMD proteins. |
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Download this section (compressed HTML)Q: Does MJ1511 have any detectable peroxidase, oxidoreductase, or disulfide exchange activity in vitro despite lacking the canonical CXXC motif?
Q: Is MJ1511 expressed under oxidative stress conditions in M. jannaschii, suggesting a role in antioxidant defense?
Q: What is the oligomeric state of MJ1511? AhpD enzymes typically form trimers or higher-order oligomers.
Q: Does MJ1511 interact with a peroxiredoxin (AhpC-like) partner in M. jannaschii?
Experiment: Express and purify recombinant MJ1511 and test for peroxidase activity using a FOX assay (ferrous oxidation-xylenol orange) with hydrogen peroxide and alkyl hydroperoxides as substrates, as done for P. aeruginosa AhpD-like protein (PMID:21615954). Also test for thiol-disulfide exchange activity. Include C17S and C107S single mutants to assess the contribution of each cysteine.
Hypothesis: MJ1511 may retain weak peroxidase or disulfide exchange activity despite lacking the canonical CXXC motif.
Type: biochemical assay
Experiment: Test purified MJ1511 for carboxymuconolactone decarboxylase activity using gamma-carboxymuconolactone as substrate, monitoring decarboxylation spectrophotometrically.
Hypothesis: MJ1511 may have a decarboxylase rather than oxidoreductase function, consistent with the CMD (carboxymuconolactone decarboxylase) family classification.
Type: enzyme activity assay
Experiment: Perform transcriptomic or proteomic analysis of M. jannaschii under oxidative stress conditions (e.g. exposure to oxygen or hydrogen peroxide) and compare MJ1511 expression with control conditions.
Hypothesis: MJ1511 is expressed under conditions of oxidative stress in M. jannaschii.
Type: transcriptomics/proteomics
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