A0BFB4 (ORF GSPATT00028266001) is an uncharacterized 381-residue protein kinase from the ciliate Paramecium tetraurelia. Residues 96-348 form a protein kinase domain, and the catalytic motifs are intact (glycine-rich loop, beta3 lysine K125, HRD catalytic loop, DFG, APE). It is therefore predicted to be an active, ATP-dependent protein serine/threonine kinase. Outside the kinase domain there is only a ~95-residue N-terminal segment with no annotated domain and a short C-terminal tail. It has none of the C-terminal regions that canonical Atg1/ULK kinases use to assemble the autophagy-initiation complex. Its classification within the kinome is uncertain. PANTHER's reference tree grafts it into the Atg1/UNC-51 family (PTHR24348), but the current PANTHER HMM assigns it to PTHR44167 (CHK2/CDC7-related kinases), and a kinase-domain distance tree does not group it robustly with Atg1/ULK proteins. Its substrates, subcellular location and biological roles have not been studied.
Summary: Membrane association is propagated from the Atg1/ULK ancestral node PTN000681272, where it reflects Atg1/ULK recruitment to autophagic membranes. A0BFB4 lacks the module that mediates that recruitment and has no transmembrane or lipid-anchor features.
Reason: The membrane IBD sits on the same Atg1/ULK node (PTN000681272) as the phagophore assembly site and autophagosome IBDs, and its seeds are Atg1/ULK proteins (ULK1, ULK2, yeast ATG1, S. pombe Atg1). Atg1/ULK proteins reach membranes through their C-terminal domain and Atg13/Atg17-FIP200 partners. A0BFB4 lacks that domain, and ciliates lack the partners (PMID:28123910). The UniProt record has no transmembrane or signal features. The node placement itself is also weak at the sequence level (see the bioinformatics results). The earlier ACCEPT treated this term as generic, but it is one of the Atg1-node localization assertions and rests on the same inheritance argument as the phagophore-site term. It is therefore marked over-annotated rather than accepted. It is not removed, because a peripheral membrane association is not contradicted.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:COMPARTMENT OR COMPLEX MISMATCHFUNCTIONAL DIVERGENCE
Sources checked:
PANTHER:PTN000681272SUPPORTS SOURCE BUT NOT TARGET
Atg1/ULK node; membrane recruitment of the seed kinases depends on the C-terminal domain and complex partners that A0BFB4 and ciliates lack.
Atg1 complex members (Atg13, Atg17, Atg29, Atg31 in the yeast Atg1 complex; Atg13, Atg101 and FIP200 in the mammalian ULK1 complex) require the C-terminal domain of Atg1 to interact and form the complex
Summary: Cytoplasm is propagated from the deep PTHR24348 family node PTN002805221, not from the Atg1-specific node. It fits a soluble kinase-domain protein with no signal peptide or transmembrane segment.
Reason: This IBD sits at the family-level node PTN002805221, the same node that supplies protein serine/threonine kinase activity. Cytoplasmic residence of these kinases does not depend on the Atg1 C-terminal module. A0BFB4 has no predicted signal peptide, transmembrane helix or organellar targeting feature, so the inference is not contradicted. No experimental localization exists for A0BFB4 (the deep-research report found none). The term is as precise as the evidence allows.
Supporting Evidence:
file:PARTE/A0BFB4/A0BFB4-deep-research-falcon.md
No direct localization data exist for protein A0BFB4.
Summary: Over-propagated. Autophagosome assembly by Atg1/ULK needs the Atg1 complex, which cannot form here. A0BFB4 lacks the Atg1 C-terminal domain, ciliates lack Atg13, Atg17, FIP200 and Atg101, and A0BFB4 does not group robustly with Atg1/ULK by sequence.
Reason: The IBD at PTN000681272 is sound for Atg1/ULK proteins. Two lines of target-specific evidence argue against inheritance here. (1) Aslan et al. surveyed ciliate genomes, including Paramecium tetraurelia, and found that every Atg1-like kinase-domain protein lacks the Atg1-specific C-terminal domain needed to form the complex. The other Atg1-complex members are also absent. The authors conclude that these proteins should not be considered Atg1 candidates without experimental work (PMID:28123910). A0BFB4 has a C-terminal tail of only 33 residues after the kinase domain. (2) Membership of the Atg1 clade is itself doubtful. The current PANTHER HMM places A0BFB4 in PTHR44167, not PTHR24348. In the kinase-domain neighbour-joining analysis, A0BFB4 grouped exclusively with the ATG1/ULK kinases in only 1 of 200 bootstrap replicates. Kinase activity is retained, but participation in autophagosome assembly is not established. It is not removed outright because ciliates do have autophagy (PMID:24280724), and whether any ciliate Atg1-like kinase contributes to it remains open.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCECOMPARTMENT OR COMPLEX MISMATCH
Sources checked:
PANTHER:PTN000681272SUPPORTS SOURCE BUT NOT TARGET
Atg1/ULK node, correct for the seeds. The A0BFB4 leaf PTN002805316 grafted below it lacks the C-terminal complex-assembly domain, and its placement conflicts with the current HMM family PTHR44167.
ciliate genomes do not encode typical Atg1 since all the candidate sequences lack an Atg1-specific C-terminal domain which is essential for Atg1 complex formation
We conclude that these kinase domain containing proteins should not be considered as Atg1 candidates without further experimental analyses, since they all lack the important C-terminal domains.
Summary: Over-propagated from the same Atg1/ULK node. No evidence ties A0BFB4 to autophagy regulation, and the inheritance argument is the same weak one behind the other autophagy rows.
Reason: The previous review left this row UNDECIDED because the term is broad enough to allow a noncanonical ciliate role. This re-review gives it the same action as the sister autophagy rows, because it rests on the same IBD source (PTN000681272) and the same weak Atg1-clade placement. The seed regulatory roles (ULK1, Drosophila Atg1) act through the Atg1 complex. Aslan et al. leave open whether any ciliate kinase-domain protein has an autophagic role (PMID:28123910). That possibility is not evidence for this protein, which has no perturbation, localization or interaction data. Ciliate autophagy-like programmed nuclear death runs through VPS34 and ATG8 (PMID:24280724), not through any characterized Atg1-like kinase. The row is kept as over-annotated rather than removed, pending Paramecium-specific data.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:FUNCTIONAL DIVERGENCE
Sources checked:
PANTHER:PTN000681272SUPPORTS SOURCE BUT NOT TARGET
The seeds regulate autophagy through the Atg1/ULK complex. No complex-independent regulatory role is documented for ciliate Atg1-like kinase-domain proteins.
Summary: Over-propagated. Atg1/ULK targeting to the phagophore assembly site depends on the C-terminal domain and partner complex, which A0BFB4 and ciliates lack.
Reason: The localization of the seed kinases (ULK1, ULK2, yeast ATG1) to the phagophore assembly site is mediated by Atg13 and Atg17/FIP200 binding to the Atg1 C-terminal domain. A0BFB4 lacks that domain, ciliates lack those partners, and A0BFB4's grouping with the Atg1/ULK clade is itself weak. No Paramecium localization data exist.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:COMPARTMENT OR COMPLEX MISMATCH
Sources checked:
PANTHER:PTN000681272SUPPORTS SOURCE BUT NOT TARGET
Atg1/ULK node. PAS targeting needs the C-terminal module, which is absent from A0BFB4.
Atg1 complex members (Atg13, Atg17, Atg29, Atg31 in the yeast Atg1 complex; Atg13, Atg101 and FIP200 in the mammalian ULK1 complex) require the C-terminal domain of Atg1 to interact and form the complex
Summary: Over-propagated autophagosome localization, for the same reasons as the phagophore assembly site row.
Reason: The localization of the seed Atg1/ULK proteins to autophagosomes depends on Atg1 complex recruitment, which cannot occur through the canonical mechanism in ciliates. A0BFB4 has no membrane-binding features, does not group robustly with Atg1/ULK, and has no localization data.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:COMPARTMENT OR COMPLEX MISMATCH
Sources checked:
PANTHER:PTN000681272SUPPORTS SOURCE BUT NOT TARGET
Atg1/ULK node. Autophagosome association of the seeds requires complex assembly that is absent in the ciliate target.
ciliate genomes do not encode typical Atg1 since all the candidate sequences lack an Atg1-specific C-terminal domain which is essential for Atg1 complex formation
file:PARTE/A0BFB4/A0BFB4-deep-research-falcon.md
No direct localization data exist for protein A0BFB4.
GO:0004674 protein serine/threonine kinase activity
IBA GO_REF:0000033
ACCEPT
Summary: Core function. It is propagated from the deep PTHR24348 node PTN002805221 and matches the intact Ser/Thr kinase catalytic machinery of A0BFB4.
Reason: This MF IBD sits at the family-level node PTN002805221 and is independent of the Atg1-specific placement debated above. A0BFB4 keeps every canonical catalytic motif (GEGTFG glycine-rich loop, K125, HRDIKPDN catalytic loop, DFG, APE) and the PROSITE Ser/Thr active-site signature. Protein serine/threonine kinase activity is also the conserved activity of PTHR44167, the family to which the current HMM assigns A0BFB4. The MF holds whichever classification is right.
Summary: Cytosol is propagated from PTN000681272, but it reflects the soluble character of these kinases rather than complex-dependent targeting. It is plausible for A0BFB4 and kept as non-core.
Reason: Unlike the phagophore and autophagosome terms, cytosolic residence of the seed kinases does not depend on the missing C-terminal module. A soluble kinase-domain protein with no targeting features is expected to reside in the cytosol. There is no direct localization evidence, and the source node is the debated Atg1/ULK node. The term is therefore kept, but not treated as part of the core description.
Supporting Evidence:
file:PARTE/A0BFB4/A0BFB4-deep-research-falcon.md
No direct localization data exist for protein A0BFB4.
Summary: True but general. The supported nucleotide is ATP, through the conserved kinase ATP-binding site.
Reason: The PROSITE ATP-binding signature and K125 identify the bound nucleotide as ATP. ATP binding (GO:0005524), which this gene already carries, is the specific supported term.
Summary: True but general. The Ser/Thr active-site signature supports the more specific protein serine/threonine kinase activity.
Reason: The PROSITE Ser/Thr kinase active-site signature (PS00108) and the HRDIKPDN catalytic loop specify Ser/Thr phosphorylation. GO:0004674, which this gene already carries, is the specific supported descendant.
Summary: ATP binding by the conserved kinase ATP site (glycine-rich loop GEGTFG and K125).
Reason: The PROSITE ATP-binding signature, the glycine-rich loop and the beta3 lysine K125 (annotated by PROSITE-ProRule as the ATP-binding residue) are all present. ATP binding is intrinsic to the kinase's catalytic activity.
Summary: True but general. Refine to protein serine/threonine kinase activity.
Reason: The kinase domain has the protein-kinase fold and the Ser/Thr active-site signature, so the supported specific term is GO:0004674, which this gene already carries.
Summary: True but very general. Refine to protein serine/threonine kinase activity.
Reason: The transferase activity of A0BFB4 is phosphotransfer from ATP to protein Ser/Thr residues. GO:0004674, already carried, is the specific supported descendant.
Predicted ATP-dependent protein serine/threonine kinase activity of a kinase domain with intact catalytic motifs. Substrates, pathway and location are unknown, and no Atg1/ULK-complex role is established.
Q: Should A0BFB4 remain a PAINT tree member of PTHR24348 below the Atg1/ULK node PTN000681272 when the current PANTHER HMM assigns it to PTHR44167:SF18? If the graft stands, can the Atg1-node BP/CC IBDs (autophagosome assembly, regulation of autophagy, phagophore assembly site, autophagosome, membrane) be blocked for ciliate kinase-domain-only descendants while the kinase MF is kept?
Q: Which PANTHER family do the many Paramecium and Tetrahymena paralogs of A0BFB4 fall into, and does a full kinome phylogeny place this ciliate expansion inside the Atg1/ULK clade, the CAMK/CHK clade, or as a ciliate-specific group?
Q: What, if anything, does the ~95-residue N-terminal segment before the kinase domain contribute (regulation, localization, partner binding)?
Suggested Experiments
Experiment: Express the recombinant kinase domain with a K125A (ATP-site lysine) control and measure autophosphorylation and phosphorylation of generic substrates (MBP, histone H1); then use peptide-library profiling to define its phosphosite motif.
Hypothesis: A0BFB4 is an active protein serine/threonine kinase.
Type: In vitro kinase assay
Experiment: Deplete A0BFB4 and its closest ohnologs by RNAi feeding during starvation and autogamy, and quantify ATG8 puncta and old-macronucleus degradation against controls.
Hypothesis: A0BFB4 contributes to a noncanonical Paramecium autophagy-like process.
Type: RNAi phenotype assay
Experiment: Express GFP-tagged A0BFB4 and image it in vegetative, starved and autogamous cells, co-imaging with an ATG8 marker.
Hypothesis: A0BFB4 localizes to the cytoplasm and not to autophagic membranes.
Type: Live-cell localization
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
A0BFB4 is an uncharacterized Paramecium protein kinase whose kinase domain (residues 96-348) retains every canonical catalytic motif, so it is expected to be an active protein serine/threonine kinase. The single ProtNLM2 prediction, protein phosphorylation, is the process that this catalytic activity carries out and is not yet annotated to the gene. No experimental study of this protein or its ORF (GSPATT00028266001) was found in PubMed.
Prediction method: ProtNLM2 · Version: UniProt 2024_06 pilot
Review rationale: The protein kinase domain (96-348) carries the PROSITE protein-kinase ATP-binding and serine/threonine-kinase active-site signatures, and motif analysis finds the glycine-rich loop, beta3 lysine K125, HRD catalytic loop, DFG and APE motifs all intact, so the protein is predicted to be a catalytically competent kinase rather than a pseudokinase. The gene review accepts protein serine/threonine kinase activity (GO:0004674) as its core function on this basis. An active protein kinase performs the phosphotransfer step of protein phosphorylation itself, so the process term follows directly from the supported activity. GO:0006468 is not among the gene's GOA annotations, and OLS4 lists no is_a or part_of path from GO:0004674 to it, so the prediction adds a novel process annotation. Support is sequence-based inference; no substrate or phosphorylation event has been observed, and the term implies nothing about the autophagy roles that the gene review marks over-annotated.
Supporting Evidence:
file:PARTE/A0BFB4/A0BFB4-uniprot.txt: "DR InterPro; IPR000719; Prot_kinase_dom. ... DR InterPro; IPR017441; Protein_kinase_ATP_BS. ... DR InterPro; IPR008271; Ser/Thr_kinase_AS. ... FT DOMAIN 96..348"