ccr1 (SPBC29A10.01) encodes the fission yeast NADPH--cytochrome P450 reductase (CPR, EC 1.6.2.4), a diflavin (FAD + FMN) reductase anchored in the endoplasmic reticulum membrane with its catalytic domains facing the cytoplasm. It transfers electrons from NADPH to microsomal cytochrome P450 enzymes, notably the sterol 14alpha-demethylase Erg11 (CYP51) and, by homology, the C-22 desaturase Erg5 and squalene epoxidase Erg1, and so supports ergosterol biosynthesis. Deletion is viable but makes cells hypersensitive to azoles, terbinafine and fenpropimorph, and causes secondary defects in cell wall integrity, vacuole fusion and calcium/calcineurin signalling. Ccr1 microsomal reductase activity is inhibited by tamoxifen. Ccr1 also supports heterologously expressed human P450s in S. pombe.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003958 NADPH-hemoprotein reductase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT node PTN000453765 (CPR clade) seeded by experimentally characterised CPRs including S. cerevisiae Ncp1, rat Por, plant ATR1/ATR2 and Ccr1 itself. Ccr1 is a canonical member of the CPR subfamily (PTHR19384:SF17) and has its own experimental support for the activity. Reason: The phylogenetic inference agrees with the S. pombe experimental data; Ccr1 appearing among the sources reflects its own experimental grounding, not circularity. Supporting Evidence: PMID:32571823 the results showed that TAM inhibited NADPH-cytochrome P450 reductase activities in a dose-dependent manner |
| GO:0003958 NADPH-hemoprotein reductase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated annotation from the CPR InterPro entry IPR023208, HAMAP/UniRule MF_03212 and EC 1.6.2.4 / RHEA:24040. Correct for Ccr1, which is a full-length diflavin CPR. Reason: Correct EC-based mapping, consistent with S. pombe experimental data. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Reaction=2 oxidized [cytochrome P450] + NADPH = 2 reduced [cytochrome |
| GO:0003958 NADPH-hemoprotein reductase activity | IMP PMID:23737303 Coexpression of CPR from various origins enhances biotransfo... | ACCEPT | Summary: Neunzig et al. 2013 coexpressed ccr1 (or human or Ammi majus CPR) with seven human microsomal CYPs in S. pombe and found that ccr1 coexpression raised biotransformation activity, e.g. CYP2D6 was most active with ccr1. The cached record is abstract-only; the curator's IMP reflects a gene-dosage manipulation that changes P450 output, consistent with Ccr1 donating electrons to P450s. Reason: Defers to the PomBase curator, who read the full text; the observation is consistent with the established CPR activity. Supporting Evidence: PMID:23737303 CYP2D6 displayed its highest activity when coexpressed with ccr1 |
| GO:0003958 NADPH-hemoprotein reductase activity | TAS PMID:32571823 NADPH-Cytochrome P450 Reductase Ccr1 Is a Target of Tamoxife... | ACCEPT | Summary: Liu et al. 2020 measured NADPH-cytochrome c reductase activity in S. pombe microsomes, attributed it to Ccr1, and showed dose-dependent inhibition by tamoxifen. Reason: The paper states and measures the activity for Ccr1 directly in S. pombe microsomes. Supporting Evidence: PMID:32571823 the Ccr1 activity in the microsomal enzyme solution was determined by using an NADPH-cytochrome c reductase assay kit |
| GO:0005737 cytoplasm | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: UniRule-derived location. Ccr1 is an ER-membrane protein facing the cytoplasm, and the ER membrane is part of the cytoplasm in GO, so this is true but uninformative. Reason: Correct but very general; ER membrane is the informative location. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005739 mitochondrion | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: UniRule MF_03212 location, templated on S. cerevisiae Ncp1, which is found in mitochondrial outer membrane proteomes. No S. pombe data place Ccr1 in mitochondria; genome-wide YFP localisation in S. pombe recorded it at the ER. Reason: Plausible secondary location by homology (consistent with the NCP1 review), not tested in S. pombe and not the site of the core activity. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Mitochondrion outer membrane {ECO:0000255|HAMAP-Rule:MF_03212} |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Subcellular-location keyword mapping from the HAMAP-assigned "Mitochondrion outer membrane" line, which derives from the budding-yeast template rather than S. pombe evidence. Reason: Plausible secondary location by homology only; ER membrane is the primary site. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Mitochondrion outer membrane {ECO:0000255|HAMAP-Rule:MF_03212} |
| GO:0005783 endoplasmic reticulum | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: Genome-wide YFP-tagged ORFeome localisation in S. pombe (Matsuyama et al. 2006) placed Ccr1 at the ER. Abstract-only in cache, but the high-throughput localisation is the stated method. Reason: Direct S. pombe localisation data, consistent with ER-membrane CPR; ER membrane is more precise. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Combined automated ER-membrane location (UniRule and subcellular-location mapping). Ccr1 has a single N-terminal membrane anchor like all microsomal CPRs, and the ER localisation is supported in S. pombe by the ORFeome screen. Reason: Core location of the reductase activity. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005789 endoplasmic reticulum membrane | ISS GO_REF:0000024 | ACCEPT | Summary: PomBase curator transfer from S. cerevisiae Ncp1 (P16603), whose ER-membrane location is experimentally established. Also used as the occurs_in of the Ccr1 activity in the PomBase ergosterol GO-CAM. Reason: Core location; consistent with the S. pombe ER localisation and the Ncp1 review. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005829 cytosol | IBA GO_REF:0000033 | REMOVE | Summary: IBA from a deep PTHR19384 node (PTN000453956) seeded mainly by soluble diflavin reductases (nitric oxide synthases, methionine synthase reductase MTRR, NDOR1, S. cerevisiae Tah18) together with POR. Ccr1 belongs to the membrane-anchored CPR subfamily and acts on the cytoplasmic face of the ER membrane, not free in the cytosol. Reason: The cytosolic localisation is a property of the soluble subfamilies at this node and does not apply to the TM-anchored CPR; same conclusion as the S. cerevisiae NCP1 review. Propagation Review Root cause: PROPAGATION BAD Failure modes: COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000453956 Β· PTN000453956 SUPPORTS SOURCE BUT NOT TARGET Cytosolic location holds for soluble NOS/MTRR/NDOR1/Tah18 members, but Ccr1 is a TM-anchored CPR acting at the ER membrane. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt CC -!- SUBCELLULAR LOCATION: Endoplasmic reticulum membrane |
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: HAMAP-rule "Cell membrane" location templated on S. cerevisiae Ncp1, which is found in plasma membrane fractions where it supports ferrireductase activity. Not examined in S. pombe. Reason: Homology-based secondary location only; not the site of the sterol pathway activity. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Cell membrane {ECO:0000255|HAMAP-Rule:MF_03212}; Single-pass membrane |
| GO:0006696 ergosterol biosynthetic process | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule-based process. Ccr1 reduces the ER P450s of the sterol pathway (Erg11, Erg5); its loss makes S. pombe hypersensitive to inhibitors of several ergosterol enzymes. Reason: Core process; Ccr1 contributes the electron-transfer step that the P450 oxidations depend on. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt heme oxygenase and cytochrome B5. Involved in ergosterol biosynthesis. PMID:32571823 the Ξ ccr1 cells exhibited hypersensitivity to all these drugs |
| GO:0006696 ergosterol biosynthetic process | ISS GO_REF:0000024 | ACCEPT | Summary: PomBase transfer from S. cerevisiae Ncp1, whose disruption lowers ergosterol and whose purified protein reconstitutes CYP51 and CYP61 activity. Supported in S. pombe by azole and terbinafine hypersensitivity of the deletion. Reason: Core process; consistent with the NCP1 review and the S. pombe phenotypes. Supporting Evidence: PMID:32571823 which functions by disrupting ergosterol biosynthesis through inhibition of the cytochrome P450-dependent enzyme lanosterol 14-Ξ±-demethylase |
| GO:0010181 FMN binding | IBA GO_REF:0000033 | ACCEPT | Summary: FMN binding is an ancestral property of the whole diflavin reductase family (flavodoxin module) and is conserved in Ccr1, which has the Flavodoxin_1 domain. Reason: Correct cofactor binding inherited from the family root; Ccr1 keeps the flavodoxin domain. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Note=Binds 1 FMN per monomer. |
| GO:0010181 FMN binding | IEA GO_REF:0000120 | ACCEPT | Summary: InterPro flavodoxin-like domain (IPR001094, IPR008254) and UniRule mapping to FMN binding. Correct for Ccr1. Reason: Correct cofactor binding. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Note=Binds 1 FMN per monomer. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MODIFY | Summary: Generic InterPro2GO mapping from the FAD/NAD-binding and flavoprotein reductase domains. Correct but much less informative than the established NADPH-hemoprotein reductase activity. Reason: Replace with the specific activity, which Ccr1 already carries. Proposed replacements: NADPH-hemoprotein reductase activity Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Reaction=2 oxidized [cytochrome P450] + NADPH = 2 reduced [cytochrome |
| GO:0050660 flavin adenine dinucleotide binding | IBA GO_REF:0000033 | ACCEPT | Summary: FAD binding is ancestral to the diflavin reductase family (FNR-like module) and conserved in Ccr1 (FAD_binding_1 and NAD_binding_1 domains). Reason: Correct cofactor binding. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Note=Binds 1 FAD per monomer. |
| GO:0050660 flavin adenine dinucleotide binding | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule mapping to FAD binding; correct for the CPR family. Reason: Correct cofactor binding. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Note=Binds 1 FAD per monomer. |
| GO:0050661 NADP binding | IEA GO_REF:0000104 | ACCEPT | Summary: UniRule mapping to NADP binding. NADPH is the electron donor of the CPR reaction and binds the C-terminal FNR-like module. Reason: Correct substrate binding for an NADPH-dependent reductase. Supporting Evidence: file:SCHPO/ccr1/ccr1-uniprot.txt Reaction=2 oxidized [cytochrome P450] + NADPH = 2 reduced [cytochrome |
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Download this section (compressed HTML)Q: Does S. pombe Ccr1 supply electrons to Erg5 (CYP61) and Erg1 in vivo, as Ncp1 does in budding yeast, and how much can the cytochrome b5 route (Cbr1 with Cyb502/Oca8) compensate for its loss at Erg11?
Experiment: Sterol profiling (GC-MS) of ccr1 deletion, cbr1 deletion and double mutants, with and without azole, to quantify accumulation of lanosterol and ergosta-5,7-dienol and so separate Ccr1 support of Erg11 from support of Erg5.
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