maiA

Summary: InterPro2GO (IPR005955 GST zeta) annotation to the root term catalytic activity.

Reason: True but uninformative; entailed by the accepted maleylacetoacetate isomerase activity (GO:0016034).

Summary: Glutathione transferase activity inferred by PAINT at PTN001344486 (zeta-class GST/MAAI node), from fly GstZ, human GSTZ1 and E. coli sources.

Reason: MaiA is a zeta-class glutathione transferase family member and binds glutathione as cofactor; zeta-class enzymes (e.g. human GSTZ1) have measurable GST/dehalogenase-type activity besides the isomerase. Nothing in the A. nidulans literature tests or excludes conjugating activity for MaiA, and the PAINT node placement covers it without any evidence of loss, so the IBA is retained. It is not the physiological function: the only activity shown for MaiA, and the one whose loss gives the pathway phenotype, is glutathione-dependent cis-trans isomerization of maleylacetoacetate (PMID:9417084). The split with P. putida HmgC (Q88E49), where the same family-level term is MARK_AS_OVER_ANNOTATED, is deliberate: MaiA sits in the eukaryotic SF4 clade with human GSTZ1, whose transferase activity is measured, whereas HmgC sits in the bacterial SF21 maiA/maleylpyruvate-isomerase branch, whose structurally characterized member uses glutathione as a regenerated cofactor.

Summary: Cytoplasm, from InterPro and the UniProt subcellular-location vocabulary (UniProt: Cytoplasm, by similarity).

Reason: The homogentisate pathway enzymes are soluble cytoplasmic enzymes; UniProt assigns MaiA to the cytoplasm by similarity, and MaiA has no predicted targeting or transmembrane features. No direct localization experiment exists for A. nidulans MaiA, so cytoplasm (rather than the more specific cytosol) is the appropriate level.

Summary: Mitochondrion (is_active_in) inferred at PAINT node PTN000137159 from mammalian GSTZ1 (human, mouse, rat) data.

Reason: Mitochondrial localization of zeta-class GST has been reported only for mammalian GSTZ1, and these mammalian proteins are the only sources of the IBD. In mammals the mitochondrial matrix pool is a minor fraction alongside the predominant cytosolic enzyme, and it is the cytosolic pool that carries out homogentisate-pathway isomerization. I found no localization data for A. nidulans MaiA or other fungal MAAIs, UniProt places it in the cytoplasm by similarity, and the protein has no predicted targeting features. Extending a minor, mammal-documented mitochondrial pool to the fungal enzyme is therefore more than the evidence supports; the row is kept as a likely over-annotation rather than removed, because a mitochondrial fraction has not been tested and excluded.

Summary: L-phenylalanine catabolic process, IBA at PTN001344486 whose only listed source is MaiA (O43123) itself.

Reason: MaiA catalyses the isomerization of maleylacetoacetate to fumarylacetoacetate, a step of the common part of phenylalanine/phenylacetate catabolism. The target appearing as the IBD source is the expected marker of its own experimental grounding (PMID:9417084).

Summary: Direct assay: recombinant MaiA has MAAI activity, a step of phenylalanine catabolism.

Reason: The catalytic step performed by MaiA is part of phenylalanine catabolism, so the IDA activity evidence supports direct participation in the process.

Summary: UniPathway UPA00139 (L-phenylalanine degradation) mapping.

Reason: Consistent with the experimental data: maiA disruption prevents growth on phenylalanine and phenylacetate (PMID:9417084).

Summary: maiA disruption prevents growth on phenylalanine and phenylacetate, abolishes MAAI activity, and causes phenylalanine toxicity and accumulation of 2,4-dioxohept-2-enoic acid.

Reason: Direct genetic evidence that MaiA is required for, and acts within, phenylalanine catabolism; together with the enzyme assay it identifies the step MaiA performs.

Summary: Glutathione metabolic process inferred at PTN001344486 from fly GstZ and human GSTZ1 sources.

Reason: MaiA uses glutathione as a non-consumed cofactor for the cis-trans isomerization of maleylacetoacetate; it does not synthesise, degrade or otherwise metabolise glutathione as part of its demonstrated function (PMID:9417084). The process term probably reflects conjugating (GST) activity of animal zeta-class enzymes rather than the isomerase role, and there is no evidence that MaiA participates in glutathione metabolism in A. nidulans. Retained as an over-annotation rather than removed because it rests on a PAINT node placement that has not been shown to be wrong for fungi.

Summary: InterPro2GO (IPR005955) annotation to aromatic amino acid metabolic process.

Reason: True but entailed by the accepted, more specific L-phenylalanine catabolic process (GO:0006559).

Summary: Maleylacetoacetate isomerase activity at PAINT node PTN001344486, seeded by MaiA itself, human GSTZ1, mouse Gstz1 and Arabidopsis GSTZ1.

Reason: Core function, experimentally established for MaiA (PMID:9417084). The appearance of O43123 itself among the IBD sources reflects its own IDA/IMP data and is expected.

Summary: Recombinant MaiA expressed in E. coli has MAAI activity.

Reason: Direct biochemical demonstration of the activity in the founding characterization of a MAAI gene from any organism; UniProt records the reaction with experimental evidence from this paper.

Summary: Electronic annotation from RHEA:14817 / EC 5.2.1.2 mapping.

Reason: Agrees with the experimental evidence for MaiA and with its zeta-class GST family membership and maiA TIGRFAM signature.

Summary: maiA disruption results in absence of MAAI activity in vitro.

Reason: Loss of the measured enzyme activity in extracts of the disruptant directly links the activity to the maiA gene product.

Summary: MaiA catalyses the maleylacetoacetate isomerization step of homogentisate catabolism; maiA is clustered with hmgA and fahA.

Reason: MaiA isomerizes maleylacetoacetate, the product of HmgA ring cleavage, to fumarylacetoacetate for FahA, so it performs one of the three catalytic steps of homogentisate catabolism (participation, not mere requirement). GO:1902000 is not a subclass of L-phenylalanine catabolic process. Added for consistency with HmgA and FahA in the same gene cluster, which both carry the term.