Cao1 (SPAC2E1P3.04, formerly spao1) is the single catalytically active copper/topaquinone (TPQ) amine oxidase of fission yeast, a member of the copper amine oxidase family (PANTHER PTHR10638, subfamily SF86) that also contains the Hansenula polymorpha methylamine oxidase. It catalyzes the oxygen-dependent oxidative deamination of primary amines to the corresponding aldehyde, ammonia and hydrogen peroxide, with ethylamine, putrescine and 1,8-diaminooctane among its preferred substrates, and allows primary amines such as ethylamine to be used as nitrogen sources. Activity requires copper; conserved C-terminal histidines are needed for activity, and the active-site tyrosine (Tyr407) in the conserved Asn-Tyr-Asp/Glu-Tyr motif is expected to be converted autocatalytically to TPQ. In vegetative cells Cao1 is cytosolic and excluded from the nucleus, and it obtains copper via the Ctr4/Ctr5 uptake system and largely through the Atx1 metallochaperone, with which it interacts. During meiosis Cao1 accumulates within forespores, where its activity depends on copper imported by the forespore membrane transporter Mfc1. The paralog Cao2 is expressed but shows no detectable amine oxidase activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005507 copper ion binding | IBA GO_REF:0000033 | ACCEPT | Summary: Copper is the essential catalytic metal of Cao1, inherited from the copper amine oxidase ancestor. Reason: The PAINT IBD at PTN000067313 places copper binding at the root of the copper amine oxidase family, and Cao1 sits in subfamily SF86 within that clade with all copper-coordinating histidines conserved. Target-specific evidence agrees - copper chelation or loss of copper delivery abolishes Cao1 activity without lowering Cao1 protein levels, and mutation of C-terminal histidines predicted to coordinate copper abolishes activity. The IBA and IEA rows make the same claim and are accepted together. Supporting Evidence: PMID:18723604 Site-directed mutagenesis identified three histidine residues within the C-terminal region of Cao1 that are necessary for amine oxidase activity. PMID:18723604 The requirement for copper is absolute for their activity. PMID:18723604 the Atx1 metallochaperone represents an important source of copper for Cao1. |
| GO:0005507 copper ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: Copper is the essential catalytic metal of Cao1. Reason: InterPro copper amine oxidase signatures (IPR000269 and its N2/N3/catalytic domain entries) correctly place Cao1 in the copper amine oxidase family, and target mutagenesis and copper-delivery experiments confirm the copper requirement. Consistent with the IBA row for the same term. Supporting Evidence: PMID:18723604 Site-directed mutagenesis identified three histidine residues within the C-terminal region of Cao1 that are necessary for amine oxidase activity. file:SCHPO/cao1/cao1-uniprot.txt CC -!- SIMILARITY: Belongs to the copper/topaquinone oxidase family. |
| GO:0005737 cytoplasm | IDA PMID:18723604 Copper distributed by Atx1 is available to copper amine oxid... | MODIFY | Summary: Functional Cao1-GFP shows uniform cytosolic fluorescence and is excluded from the nucleus. Reason: The imaging shows diffuse non-nuclear signal of an activity-retaining Cao1-GFP, which is the cytosol pattern; the paper itself describes it as cytosolic. Cytoplasm is correct but less specific than the evidence supports, so the row is refined to cytosol, a term the gene already carries (HDA). Proposed replacements: cytosol Supporting Evidence: PMID:18723604 By use of direct fluorescence microscopy, Cao1-GFP exhibited uniform fluorescent staining throughout the cytosol. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | MODIFY | Summary: Cao1 is cytosolic in vegetative cells. Reason: The UniProt SubCell mapping (Cytoplasm) derives from the same imaging and HDA data; those data support the more specific cytosol term, which the gene already carries. Same refinement as the IDA row for this term. Proposed replacements: cytosol Supporting Evidence: PMID:18723604 By use of direct fluorescence microscopy, Cao1-GFP exhibited uniform fluorescent staining throughout the cytosol. |
| GO:0005829 cytosol | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: Genome-wide localization places Cao1 in the cytosol, consistent with targeted imaging. Reason: The ORFeome screen assignment agrees with the targeted localization of a functional Cao1-GFP expressed from its own promoter. Cao1 lacks a signal peptide or peroxisomal targeting signal, unlike the peroxisomal Hansenula methylamine oxidase in the same subfamily, so a cytosolic location is the vegetative site of activity. Forespore accumulation during meiosis is an additional, stage-specific location rather than a contradiction. Supporting Evidence: PMID:18723604 Thus, the absence of Cao1 from the nucleus strongly suggests that the protein is localized primarily in the cytoplasm when expressed in fission yeast. PMID:18723604 By use of direct fluorescence microscopy, Cao1-GFP exhibited uniform fluorescent staining throughout the cytosol. |
| GO:0006878 intracellular copper ion homeostasis | IMP PMID:18723604 Copper distributed by Atx1 is available to copper amine oxid... | MARK AS OVER ANNOTATED | Summary: Cao1 is a copper-requiring client enzyme, not a component of the copper homeostasis machinery. Reason: In the full text the only cao1-deletion phenotype reported is loss of amine oxidase activity; no change in cellular copper content, distribution, uptake or copper-responsive gene expression is reported for cao1 mutants. The copper-related findings of the paper concern the requirement of Ctr4/Ctr5, Cuf1 and Atx1 for loading copper onto Cao1, with Cao1 activity used as a readout of copper bioavailability. This makes Cao1 the recipient (client) of copper distribution, a necessity relationship; the work of maintaining copper homeostasis is done by the transporters and chaperones. The curator-made IMP is not removed, but it overstates Cao1's role and is not a core process. Supporting Evidence: PMID:18723604 Taken together, our analysis of mutants defective in cao1 + , cao2 + , or both genes revealed that cao1 + plays a unique role in producing amine oxidase activity in S. pombe . PMID:18723604 Collectively, these results describe the first example of the ability of Atx1 to act as a copper carrier for a molecule other than Ccc2 and its critical role in delivering copper to Cao1. |
| GO:0008131 primary methylamine oxidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Primary amine oxidase activity is the inherited core activity of the copper amine oxidase family and is directly demonstrated for Cao1. Reason: GO:0008131 (EC 1.4.3.21, RHEA:16153) is the generic primary amine oxidase activity despite its methylamine-focused label. The PAINT IBD for it sits at the family root node PTN000067313, and Cao1 descends from that node within subfamily SF86. Cao1's own experimental annotation (PomBase:SPAC2E1P3.04) is one of the descendant evidences for the node, which is expected and indicates direct grounding on the target. Cao1 retains the TPQ precursor tyrosine, the copper-ligand histidines, the catalytic base (Asp321) and the conserved disulfide, unlike the inactive paralog Cao2. Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. PMID:18723604 In contrast, Cao1 catalyzed the oxidative deamination of all of the primary amines that we have tested. |
| GO:0008131 primary methylamine oxidase activity | IDA PMID:16946276 Mechanisms of copper loading on the Schizosaccharomyces pomb... | ACCEPT | Summary: Heterologously expressed Cao1 oxidatively deaminates primary amines. Reason: Expression of Cao1 in S. cerevisiae, which has no endogenous copper amine oxidase, produces an active primary amine oxidase. The cached record is abstract-only, but the abstract states the result and the follow-up full-text paper restates it. Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. PMID:18723604 We showed that, when heterologously expressed in S. cerevisiae , only cao1 + but not cao2 + resulted in the production of an active enzyme capable of catalyzing the oxidative deamination of ethylamine |
| GO:0008131 primary methylamine oxidase activity | IDA PMID:18723604 Copper distributed by Atx1 is available to copper amine oxid... | ACCEPT | Summary: Cao1 is the source of primary amine oxidase activity in S. pombe cell extracts. Reason: Ethylamine oxidase activity is present in wild-type and cao2-deletion extracts and absent from cao1-deletion extracts, and is restored by a functional Cao1-GFP allele. Histidine point mutants abolish activity. Supporting Evidence: PMID:18723604 In contrast, no detectable CAO activity was observed with the cao1 Ξ single mutant (Fig. 3A ). PMID:18723604 Site-directed mutagenesis identified three histidine residues within the C-terminal region of Cao1 that are necessary for amine oxidase activity. |
| GO:0008131 primary methylamine oxidase activity | IDA PMID:21828039 Mfc1 is a novel forespore membrane copper transporter in mei... | ACCEPT | Summary: Cao1-GFP amine oxidase activity was measured in meiotic diploid cells. Reason: The Mfc1 study expresses an active Cao1-GFP in a cao1-deletion diploid and measures its amine oxidase activity during meiosis (strongly reduced in mfc1 deletion cells). Although the paper is titled for Mfc1, Cao1 activity is directly assayed. Supporting Evidence: PMID:21828039 As shown in Fig. 6 D , diploid cells carrying disrupted mfc1 Ξ / Ξ alleles displayed 89% less CAO activity as compared with the wild-type mfc1 +/+ cells. |
| GO:0008131 primary methylamine oxidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic assignment of primary amine oxidase activity, consistent with direct assays. Reason: The combined IEA reproduces the experimentally established activity (EC 1.4.3.21 in the UniProt record is attributed to PMID:16946276). Consistent with the IBA and IDA rows for this term. Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. |
| GO:0009308 amine metabolic process | IBA GO_REF:0000033 | MODIFY | Summary: Correct but general; Cao1 degrades primary amines. Reason: Oxidative deamination converts amines to aldehydes and ammonia, i.e. amine catabolism, and Cao1 already carries the descendant term amine catabolic process (IDA). The PAINT node is placed at the family root, where the general metabolic term is appropriate for the family as a whole; for Cao1 the catabolic child is supported. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000067313 Β· Copper amine oxidase family root node SUPPORTS TRANSFER The family-level amine metabolism IBD correctly reaches Cao1 (subfamily SF86 descends from this node); only the granularity is refined for the target, which degrades primary amines. PomBase:SPAC2E1P3.04 Β· Cao1 itself (target's own experimental annotation) SUPPORTS TRANSFER The target's own experimental amine catabolism annotation is one of the descendant evidences for the node; this is expected, not circular. Proposed replacements: amine catabolic process Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. |
| GO:0009308 amine metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Correct but general; Cao1 degrades primary amines. Reason: Same claim as the IBA row; refined to amine catabolic process, which the gene already carries. Proposed replacements: amine catabolic process Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. |
| GO:0009310 amine catabolic process | IDA PMID:16946276 Mechanisms of copper loading on the Schizosaccharomyces pomb... | ACCEPT | Summary: Cao1 catalyzes the degradative step that releases ammonia from primary amines, allowing their use as nitrogen sources. Reason: Cao1 performs the catabolic step itself (oxidative deamination). Heterologous Cao1 rescues the inability of S. cerevisiae to use ethylamine as sole nitrogen source; in S. pombe the cao1 deletion growth defect on ethylamine is described in the follow-up paper only as unpublished observation, so the process annotation rests mainly on the enzymatic reaction plus heterologous complementation. Supporting Evidence: PMID:16946276 Expression of spao1(+) resulted in the production of an active enzyme capable of catalysing the oxidative deamination of primary amines. PMID:18723604 Consistent with a role for Cao1 in the metabolism of primary amines as alternate sources of nitrogen to support growth, we have shown previously that the inability of S. cerevisiae to utilize ethylamine as the sole nitrogen source can be corrected by the heterologous expression of Cao1 from S. pombe in S. cerevisiae |
| GO:0042764 ascospore-type prospore | IDA PMID:21828039 Mfc1 is a novel forespore membrane copper transporter in mei... | ACCEPT | Summary: Active Cao1-GFP accumulates within forespores during meiosis. Reason: An activity-retaining Cao1-GFP expressed in a cao1-deletion diploid is mainly observed inside forespores 8 h after meiotic induction, coinciding with Mfc1-imported labile copper; its activity there depends on Mfc1. This is a stage-specific site of activity distinct from the vegetative cytosol. Supporting Evidence: PMID:21828039 Cao1-GFP displayed fluorescent staining that was mainly observed within the forespores |
| GO:0048038 quinone binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Cao1 carries a protein-derived topaquinone cofactor rather than binding a free quinone. Reason: The InterPro2GO mapping reflects the TPQ cofactor of copper amine oxidases. In Cao1 the TPQ precursor tyrosine (Tyr407) is conserved and, by family homology, is autocatalytically oxidized to TPQ; TPQ is a covalently modified residue of the polypeptide, so quinone binding is at best a loose cofactor-level description rather than binding of an exogenous quinone ligand. It is retained as non-core (as for other copper amine oxidases in this repository, e.g. rat Aoc1); no target-specific TPQ spectroscopy has been reported. Supporting Evidence: PMID:18723604 The first tyrosine within this sequence (indicated in bold) is known to be posttranslationally converted to TPQ by an autocatalytic mechanism ( 9 ). file:SCHPO/cao1/cao1-uniprot.txt CC Name=L-topaquinone residue; Xref=ChEBI:CHEBI:79027; |
| GO:1990748 cellular detoxification | TAS PMID:28572514 Cell-surface copper transporters and superoxide dismutase 1 ... | UNDECIDED | Summary: A detoxification role for Cao1 is not established by any accessible evidence. Reason: The cited spore-germination paper is abstract-only in the cache and its full text could not be retrieved (Europe PMC and PMC BioC returned no body text); the abstract does not mention Cao1 or amine detoxification. Cao1 oxidizes xenobiotic-type primary amines, which could be read as detoxification, but the reaction also generates hydrogen peroxide and aldehydes, and the only physiological role with experimental support is use of amines as nitrogen sources. Without access to the curator's source statement this TAS cannot be judged. Supporting Evidence: PMID:18723604 Copper amine oxidases (CAOs) have been proposed to be involved in the metabolism of xenobiotic and biogenic amines. |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: What is the physiological substrate of Cao1 in S. pombe - small aliphatic amines released during nitrogen limitation, polyamines such as putrescine, or environmental xenobiotic amines?
Q: Which factor provides the Atx1-independent route of copper loading onto Cao1?
Q: Does the hydrogen peroxide produced by forespore-localized Cao1 have any role in spore maturation, or is forespore Cao1 simply a copper sink?
Experiment: Publish quantitative growth of cao1-deletion versus wild-type and complemented strains on ethylamine, putrescine and other primary amines as sole nitrogen source, together with steady-state kinetics (Km, kcat) of purified Cao1 for these substrates.
Type: genetic and biochemical
Experiment: Confirm TPQ formation at Tyr407 by redox-cycling (NBT) staining, phenylhydrazine adduct spectroscopy or mass spectrometry of purified Cao1, and test a Y407F mutant for loss of activity.
Type: biochemical
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)