MCO14 (systematic name YHL018W) is a small (120 aa, ~14 kDa) mitochondrial protein of Saccharomyces cerevisiae belonging to the pterin-4-alpha-carbinolamine dehydratase (PCD/DCoH) family (Pfam PF01329; InterPro IPR001533/IPR036428; PANTHER PTHR12599). It carries the diagnostic PCD catalytic His-His-Pro motif and the PCD-like fold, so it is a predicted 4-alpha-hydroxytetrahydrobiopterin dehydratase (EC 4.2.1.96), the activity that regenerates tetrahydrobiopterin during aromatic amino acid hydroxylation and that additionally, in vertebrate paralogs (DCoH), moonlights as a transcriptional coactivator of HNF1. The protein is localized to mitochondria, where its precursor is imported in a membrane-potential (delta-psi)-dependent manner and assembles into a higher-molecular-weight complex. Its enzymatic activity has not been measured directly in yeast and is annotated as putative; the canonical tetrahydrobiopterin pathway and the aromatic amino acid hydroxylases that generate its expected substrate are largely absent from budding yeast, so the physiological substrate and biological role of MCO14 in yeast are not established. It is non-essential, of moderate abundance, and has no reported deletion phenotype.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006729 tetrahydrobiopterin biosynthetic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Electronic InterPro2GO annotation propagated from the PCD/DCoH family signature. The process is biologically questionable in Saccharomyces cerevisiae: budding yeast lacks the BH4-specific biosynthetic enzymes (6-pyruvoyl-tetrahydropterin synthase and sepiapterin reductase) and the aromatic amino acid hydroxylases whose reaction produces the 4a-carbinolamine that PCD regenerates. PCD's role is in regeneration/recycling during hydroxylation rather than de novo tetrahydrobiopterin biosynthesis per se, and neither the pathway nor its substrate-generating enzymes operate natively in yeast. The term is appropriate for the family but its pathway context is absent in this organism, so it is over-annotated here. Reason: Over-propagated IEA whose metazoan/bacterial pathway context (BH4 biosynthesis and aromatic amino acid hydroxylation) is largely absent from S. cerevisiae; kept as family-level context rather than removed because the fold/motif are genuinely PCD-type. |
| GO:0008124 4-alpha-hydroxytetrahydrobiopterin dehydratase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic (EC/RHEA/InterPro-based) molecular-function annotation. MCO14 has the PCD-like fold and retains the diagnostic catalytic His-His-Pro motif, so this is the single best-supported functional hypothesis for the protein and is retained as its (predicted) core molecular function. The important caveat, recorded in the knowledge_gaps, is that UniProt flags the activity as "Putative" (no enzyme assay of the yeast protein has been reported) and the physiological substrate in yeast is unknown; the annotation therefore rests on family/domain inference, not direct evidence. Reason: Defensible domain/family-based MF prediction (conserved PCD catalytic motif) and the only informative functional hypothesis for the protein; accepted as the predicted core molecular function while its putative, unproven-in-yeast status is captured in the knowledge_gaps. |
| GO:0005739 mitochondrion | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | ACCEPT | Summary: Mitochondrial localization from the genome-wide GFP-fusion dataset (Huh et al. 2003, assigned by SGD). Independently corroborated by the high-confidence mitochondrial proteome study of Morgenstern et al. 2017 (PMID:28658629), which additionally showed that the Mco14 precursor is imported in a membrane-potential-dependent manner and forms a high-molecular-weight complex. This is the best-supported and core localization for the protein. Reason: Well-supported by two independent high-throughput datasets (GFP localization and quantitative mitochondrial proteomics with import assays). |
| GO:0003674 molecular_function | ND GO_REF:0000015 | REMOVE | Summary: Root molecular_function annotation with the ND (no biological data) evidence code, recorded by SGD to indicate that no experimental molecular-function data are available for this protein. This accurately reflects the curation state: the dehydratase activity is only a family-based electronic prediction. The ND root placeholder is superseded by the more informative (if putative) GO:0008124 IEA annotation and carries no specific information. Reason: Uninformative root-term placeholder; a specific (electronic) molecular-function annotation (GO:0008124) now exists, making the ND root redundant. |
| GO:0008150 biological_process | ND GO_REF:0000015 | REMOVE | Summary: Root biological_process annotation with the ND (no biological data) evidence code. This honestly reflects that the biological role of MCO14 in yeast is not experimentally established. It is an uninformative root placeholder and conveys no specific process. Reason: Uninformative root-term placeholder; the genuine unknown biological role is captured in the knowledge_gaps section rather than by a root ND annotation. |
Loading supporting content…
Download this section (compressed HTML)Q: Is MCO14 a catalytically active pterin-4-alpha-carbinolamine dehydratase in yeast, and what is its physiological substrate given that yeast lacks the canonical tetrahydrobiopterin pathway?
Q: What is the composition of the membrane-potential-dependent high-molecular-weight complex that Mco14 assembles into after mitochondrial import?
Experiment: Express and purify recombinant P38744 and assay dehydratase activity in vitro against 4a-hydroxytetrahydrobiopterin / 4a-hydroxytetrahydropterin substrates (spectrophotometric or coupled assay), comparing to a catalytic-His mutant.
Hypothesis: MCO14 has 4a-hydroxytetrahydropterin dehydratase activity.
Type: enzyme assay
Experiment: Perform affinity purification-mass spectrometry of chromosomally tagged Mco14 from purified mitochondria under membrane-potential-permissive conditions to identify stoichiometric complex partners.
Hypothesis: MCO14 functions within a defined mitochondrial complex.
Type: affinity purification-MS
Experiment: Profile the growth/fitness of an mco14-delta strain across respiratory, oxidative-stress, amino-acid-limitation, and pterin/folate-perturbation conditions, and measure mitochondrial pteridine metabolite levels versus wild type.
Hypothesis: MCO14 is required under a specific physiological condition.
Type: phenotypic profiling / metabolomics
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The biological process in which MCO14 participates in yeast mitochondria is unknown. The family-derived tetrahydrobiopterin pathway is largely absent from S. cerevisiae, so the process the protein actually serves (metabolic, structural, or regulatory) is undetermined.
OPEN BIOLOGY BP_DARK
What is known: Established: MCO14 is a mitochondrial protein whose precursor is imported in a membrane-potential-dependent manner and forms a high-molecular-weight complex. Not established: any pathway membership; yeast lacks the BH4-specific enzymes (PTS/PTPS, sepiapterin reductase) and aromatic amino acid hydroxylases that define the family's canonical process, and no deletion or conditional phenotype has been reported (SGD lists no phenotypes).
Significance: MCO14 is a conserved-but-dark mitochondrial protein; establishing its process would connect a widespread PCD-family fold to a defined mitochondrial function and clarify what, if anything, the pterin-dehydratase chemistry does in an organism thought to lack the pathway.
What would resolve it: Phenotypic profiling of mco14-delta under diverse conditions (respiratory/oxidative/pterin stress), affinity-purification of the membrane-potential-dependent complex to identify partners, and mitochondrial pteridine metabolomics.
Gap: The composition of the high-molecular-weight, membrane-potential-dependent complex that Mco14 assembles into is unknown; no specific interaction partner has been curated.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Established: blue-native and import assays show Mco14 forms a distinct high-molecular-weight complex after inner-membrane import. Not established: the identity of the partner subunit(s); the ~97 SGD interactions are high-throughput and non-specific.
Significance: Identifying complex partners would place MCO14 in a functional module and is the most tractable route to its in-vivo role.
What would resolve it: Reciprocal affinity purification-MS of tagged Mco14 from isolated mitochondria under membrane-potential-permissive conditions.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)