CG8745 encodes a 494-residue class-III pyridoxal 5'-phosphate (PLP)-dependent enzyme of the AGXT2-related family, with the PLP-binding lysine (K291) conserved. Phylogenetically it is the single Drosophila representative of the lineage that in vertebrates gave rise to two ammoniophospholyases, ethanolamine-phosphate phospho-lyase (ETNPPL) and 5-phosphohydroxy-L-lysine phospho-lyase (PHYKPL), which eliminate phosphate and ammonia from phosphoethanolamine and phosphohydroxylysine respectively. CG8745 is therefore predicted to be a PLP-dependent phospho-lyase acting on a phosphorylated amino compound, but its substrate, its subcellular location and its physiological role have not been tested in flies. Despite its historical "alanine-glyoxylate aminotransferase 2-like" name, its closest characterised relatives do not act as transaminases. The only direct fly data are transcriptional, including an expression association with nicotine resistance.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: PLP binding is well supported by the conserved class-III PLP-enzyme fold and the conserved Schiff-base lysine. Reason: CG8745 carries the Aminotrans_3 (PF00202) domain and the PROSITE class-III aminotransferase PLP-attachment signature, and K291 aligns with the PLP lysine of human ETNPPL (K278) and PHYKPL (K278) in the re-review alignment. Every characterised member of the family uses PLP. This is a cofactor-binding function rather than the catalytic activity itself, but it is a core, as-specific-as-warranted feature. Supporting Evidence: file:DROME/CG8745/CG8745-uniprot.txt aminotransferase family. {ECO:0000305}. file:DROME/CG8745/CG8745-bioinformatics/RESULTS-rereview.md The PLP-binding lysine is conserved: CG8745 K291 (the UniProt MOD_RES N6-(pyridoxal phosphate)lysine) |
| GO:0035094 response to nicotine | IEP PMID:17237783 Quantitative trait transcripts for nicotine resistance in Dr... | KEEP AS NON CORE | Summary: Transcript-abundance association with nicotine resistance; an expression observation, not a mechanistic role. Reason: PMID:17237783 scanned adult female head transcripts for association with nicotine resistance. The cached record is abstract-only and names ornithine aminotransferase as the strongest hit; the FlyBase curator who made this IEP read the full gene tables, so the row is not overruled. An IEP "response to" annotation only records that transcript level varies with the treatment or trait; it does not say that CG8745 participates in nicotine detoxification. It is retained as non-core and should not be used to infer function. Supporting Evidence: PMID:17237783 We performed a scan for such quantitative trait transcripts in adult female heads of the fruit fly (Drosophila melanogaster) that might explain variation for nicotine resistance. |
| GO:0050459 ethanolamine-phosphate phospho-lyase activity | ISS GO_REF:0000024 | MODIFY | Summary: The phospho-lyase chemistry is well supported phylogenetically, but the specific substrate (phosphoethanolamine) is not; generalise to the parent term. Reason: The ISS donor is human ETNPPL (Q8TBG4), which purified enzyme assays show converts phosphoethanolamine to ammonia, phosphate and acetaldehyde (PMID:22241472). The re-review alignment and tree place CG8745 basal to the vertebrate clade containing both ETNPPL (PANTHER SF1, 54% identity) and its paralog PHYKPL (SF6, 50-51% identity), which performs the same elimination on 5-phosphohydroxy-L-lysine. CG8745 is thus a co-ortholog of both enzymes, and sequence similarity cannot pick one substrate. The PAINT curator placed GO:0050459 at a Euteleostomi node (PTN002904331) that does not include CG8745, which is consistent with this. CG8745 itself sits in the mixed PANTHER SF13, alongside a bacterial decarboxylase and racemase, so subfamily membership cannot be used for transfer either. The supported claim is the chemistry that ETNPPL and PHYKPL share, a PLP-dependent carbon-oxygen lyase that eliminates phosphate. The generalisation is GO:0016838, the direct parent of GO:0050459. Proposed replacements: carbon-oxygen lyase activity, acting on phosphates Supporting Evidence: PMID:22241472 AGXT2L1 catalyzed a similar reaction on phosphoethanolamine, converting it to ammonia, inorganic phosphate, and acetaldehyde. PMID:22241472 The phosphorylation product made by this enzyme was metabolized by AGXT2L2, which converted it to ammonia, inorganic phosphate, and 2-aminoadipate semialdehyde. file:DROME/CG8745/CG8745-bioinformatics/RESULTS-rereview.md CG8745 is about equally similar to the two vertebrate ammoniophospholyase paralogs, ETNPPL (54%) and PHYKPL (50-51%), and clearly less similar to the AGXT2 transaminases (37-42%). |
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Download this section (compressed HTML)Q: Is the physiological substrate of CG8745 phosphoethanolamine, 5-phosphohydroxy-L-lysine, or both, given that the fly protein predates the vertebrate ETNPPL/PHYKPL duplication?
Q: Does Drosophila encode a 5-hydroxylysine kinase (HYKK/AGPHD1 ortholog)? Without one, 5-phosphohydroxy-L-lysine would be an unlikely physiological substrate for CG8745.
Experiment: Purify recombinant CG8745 and assay ammonia, phosphate and aldehyde release from phosphoethanolamine and 5-phosphohydroxy-L-lysine (with a K291A mutant as control) to determine substrate preference and kinetics.
Experiment: Measure phosphoethanolamine and phosphohydroxylysine in CG8745 null flies by targeted metabolomics, and determine subcellular localisation by endogenous tagging.
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