A0A8J1IYX6 (LOC101732819) is an uncharacterized 424-residue protein serine/threonine kinase of the AGC kinase group in Xenopus tropicalis. It consists of a long intrinsically disordered N-terminal region rich in basic and acidic residues (approximately residues 1-103), a single protein kinase domain (residues 113-366) and an AGC-kinase C-terminal extension (residues 367-424). The catalytic domain is most similar to those of the novel protein kinase C isoforms (about 41-43% identity to PKC theta and PKC delta) and, in a distance tree, branches at the base of the PKC/PKN clade. It is not a PKC delta ortholog: X. tropicalis has separate prkcd and prkcq genes (about 88% identity to their human orthologs over the same region), and A0A8J1IYX6 lacks the C1 diacylglycerol/phorbol-ester-binding and C2-like regulatory domains that define PKCs. The automated name "Protein kinase C delta type" therefore reflects kinase-domain similarity only. The ATP-binding lysine (K142), the HRD catalytic aspartate (D235) and the DFG magnesium-binding aspartate (D253) are retained. The activation-loop threonine that PDK1 phosphorylates in most AGC kinases is replaced by glycine (G269), and no C-terminal hydrophobic motif is recognisable. Regulation of this kinase may therefore differ from canonical AGC kinases. No experimental characterization has been published. Its function as an ATP-dependent protein serine/threonine kinase, acting in the cytoplasm and possibly the nucleus, is inferred from domain architecture, conserved catalytic motifs and phylogenetic placement in the broad AGC kinase family PTHR24351. That family includes the S6K/RSK/MSK, AKT, SGK, PKN and PKC kinases.
Summary: PAINT phylogenetic inference places nuclear activity on node PTN008614470, a Eukaryota-level node of the broad AGC kinase family PTHR24351. The descendant experimental evidence comes from fission yeast (PomBase:SPCC24B10.07), budding yeast (SGD:S000004710), trypanosome (Q582V7) and pig AKT1 (G9BWQ1). Several branches of the family act at least partly in the nucleus, including RSK/MSK, AKT and some PKC isoforms. Nuclear activity is therefore a plausible inherited property of this uncharacterized PKC-like member. The target has no annotated nuclear-localization signal, although its basic N-terminal region could contain one.
Reason: The IBA is a considered PAINT judgment, and nothing specific to the target argues for loss, so the annotation is kept. It is kept as non-core rather than accepted. In PTHR24351 nuclear activity is a context-dependent property of particular branches, not a defining one: many members act mainly at the plasma membrane or in the cytoplasm. The family review (PTHR24351-review.yaml) rates this node assessment UNRESOLVED. The target also sits on a divergent PKC-like branch, which is not the RSK/MSK or fungal lineage behind most of the nuclear evidence. Cytoplasm is the better-supported site of action.
Propagation Review
Root cause:NO FAILURE NON CORE
Sources checked:
PANTHER:PTN008614470 · PTHR24351 AGC-family localization node (Eukaryota) SUPPORTS TRANSFER
Node asserts is_active_in nucleus (IBD, paint snapshot 20260828); see PTHR24351-review.yaml, where this node is assessed UNRESOLVED. Nuclear localization is the least conserved of the properties propagated from this node, and the target's own clade (PKC-like, per A0A8J1IYX6-bioinformatics/RESULTS-rereview.md) is not the source of the nuclear evidence.
PomBase:SPCC24B10.07 · fission yeast PTHR24351-family kinase SUPPORTS TRANSFER
nuclear-localized fungal seed of the node.
UniProtKB:Q582V7 · Trypanosoma brucei Ser/Thr kinase (putative) SUPPORTS TRANSFER
SGD:S000004710 · budding yeast PTHR24351-family kinase SUPPORTS TRANSFER
Summary: PAINT phylogenetic inference (node PTN008614470) places cytoplasmic activity on a Eukaryota-level node of the AGC kinase family PTHR24351. Members of this family, including the S6Ks, RSKs, AKTs, SGKs and PKCs, are soluble kinases that act in the cytoplasm, often recruited to membranes. The target has no signal peptide, transmembrane segment or organellar targeting feature, which fits a soluble cytoplasmic kinase.
Reason: Cytoplasmic activity is a conserved property across the family from which this annotation is propagated, the family review assesses the node as SOUND, and nothing in the target sequence contradicts it. The PAINT inference is retained as the best-supported site of action.
Propagation Review
Root cause:NO FAILURE NON CORE
Sources checked:
PANTHER:PTN008614470 · PTHR24351 AGC-family localization node (Eukaryota) SUPPORTS TRANSFER
Node asserts is_active_in cytoplasm (IBD, paint snapshot 20260828); assessed SOUND in PTHR24351-review.yaml. Cytoplasm is the default and best-supported compartment for the soluble AGC kinases of this family.
PomBase:SPCC24B10.07 · fission yeast PTHR24351-family kinase SUPPORTS TRANSFER
UniProtKB:Q582V7 · Trypanosoma brucei Ser/Thr kinase (putative) SUPPORTS TRANSFER
UniProtKB:Q8I4W3 · Plasmodium falciparum RAC-beta (Akt-like) kinase SUPPORTS TRANSFER
GO:0004674 protein serine/threonine kinase activity
IBA GO_REF:0000033
ACCEPT
Summary: The protein carries a complete protein kinase domain (residues 113-366) with the PROSITE serine/threonine-kinase active-site signature (PS00108), an ATP-binding-site signature (PS00107) and an AGC-kinase C-terminal domain. The PAINT node PTN008614469 covers the whole AGC family PTHR24351 and is seeded by many experimentally characterized active kinases. These include human RSK/MSK/S6K kinases (UniProtKB:Q15418, O75582, O75676, P23443, Q9UBS0) and mouse, rat, fly, yeast, fission yeast, Dictyostelium, Plasmodium and plant members. Protein serine/threonine kinase activity is the shared molecular function of the family, including the PKC/PKN branch, which is where the target's catalytic domain is closest (RESULTS-rereview.md).
Reason: This is the primary molecular function. It is inferred from domain architecture, from conserved catalytic motifs and from placement within a family in which serine/threonine kinase activity is experimentally established in many descendants. The family review (PTHR24351-review.yaml) assesses the node as SOUND. The target retains the complete catalytic machinery: the VAIK beta-3 lysine (K142, which is its own UniProt ATP-binding feature), the HRD catalytic aspartate (D235, in motif IHRDLKPDN at 232) and the DFG magnesium-binding aspartate (D253, in motif ICDFG at 251). The activation-loop phospho-acceptor threonine of AGC kinases (PKC delta T507) is a glycine in the target (G269). This could change how the kinase is activated or how active it is. It does not remove a catalytic residue, so it is not grounds to reject the inherited activity. It is recorded as an open question.
Propagation Review
Root cause:NO FAILURE CORE
Sources checked:
PANTHER:PTN008614469 · PTHR24351 AGC-family node for protein Ser/Thr kinase activity SUPPORTS TRANSFER
IBD node (paint snapshot 20241120) seeded by experimentally characterized active kinases across the family; assessed SOUND in PTHR24351-review.yaml. The target is not among the seeds (it is uncharacterized), so there is no self-source to adjudicate.
UniProtKB:P23443 · human S6K1 (RPS6KB1) SUPPORTS TRANSFER
Best-characterized single-kinase-domain member; anchors the family catalytic_core residue site (VAIK K123 = UniProt BINDING/ATP, HRD D218 = UniProt ACT_SITE proton acceptor).
UniProtKB:Q15418 · human RSK1 (RPS6KA1) SUPPORTS TRANSFER
active member; N-terminal kinase-domain HRD aspartate D187 verified.
UniProtKB:O75582 · human MSK1 (RPS6KA5) SUPPORTS TRANSFER
UniProtKB:Q8I4W3 · Plasmodium falciparum RAC-beta (Akt-like) kinase SUPPORTS TRANSFER
Summary: The kinase binds ATP as its phosphate donor, so nucleotide binding is true. It is, however, a very broad parent of the ATP binding (GO:0005524) annotation that is also present.
Reason: True but uninformative. It is entailed by GO:0005524 ATP binding (kept as non-core in this review), which is supported by the target's own UniProt ATP-binding site feature.
Summary: The protein has protein kinase activity, but this term is the parent of the more specific GO:0004674 protein serine/threonine kinase activity, which is also annotated by IBA and IEA. The InterPro signature behind this annotation (IPR008271) is itself the serine/threonine-kinase active-site signature.
Reason: True but entailed by the accepted GO:0004674 protein serine/threonine kinase activity. The sequence carries the Ser/Thr-kinase active-site signature, not a tyrosine-kinase signature.
Supporting Evidence:
file:XENTR/A0A8J1IYX6/A0A8J1IYX6-uniprot.txt
PROSITE; PS00108; PROTEIN_KINASE_ST
GO:0004674 protein serine/threonine kinase activity
IEA GO_REF:0000120
ACCEPT
Summary: The same claim as the IBA row, here derived from InterPro domain signatures (IPR000961 AGC-kinase C-terminal), the EC mapping and UniRule. The AGC-kinase C-terminal domain and the Ser/Thr active-site signature together identify an AGC-group protein serine/threonine kinase.
Reason: Consistent with the IBA row and with the retained catalytic residues. The independent sequence-signature evidence reinforces the core molecular function.
Summary: The kinase binds ATP as the phosphate donor for its catalytic reaction. The UniProt entry records an ATP-binding site at K142 within the kinase domain, supported by the protein kinase ATP-binding-site signature (IPR017441).
Reason: Accurate and mechanistically required. It is a binding property inherent to the kinase reaction, which GO:0004674 captures, and not a separate core function.
Summary: A very broad parent term covering all kinase activities, including protein, lipid and sugar kinases. The protein is a protein serine/threonine kinase, and GO:0004674 is already annotated and accepted.
Reason: True but entailed by the accepted GO:0004674 protein serine/threonine kinase activity.
Summary: The broadest ancestor for transferases. The protein is a phosphotransferase, so the term is true, but it has no informative content.
Reason: True but entailed by the accepted GO:0004674 protein serine/threonine kinase activity.
Core Functions
ATP-dependent protein serine/threonine kinase of the AGC group, with a catalytic domain related to the PKC/PKN branch, that transfers the gamma-phosphate of ATP to serine or threonine residues of substrate proteins. Its substrates, upstream activators and biological roles are unknown. It lacks the PKC C1/C2 regulatory domains and the activation-loop phospho-threonine. By phylogenetic inference it acts in the cytoplasm.
Q: Is LOC101732819 an active kinase despite having glycine in place of the activation-loop phospho-acceptor threonine, and if so, what activates it, given that it has no C1/C2 domains to respond to diacylglycerol or calcium?
Q: How far does this PKC-like single-domain kinase extend across species? Is it an amphibian-specific duplicate, or part of an older lineage missing from mammals? A curated phylogeny with PANTHER subfamily placement would settle which characterized kinases its properties can be inferred from.
Suggested Experiments
Experiment: Express recombinant A0A8J1IYX6, run in vitro kinase assays with generic substrates (myelin basic protein, histone H1, PKC substrate peptides), and include a K142R kinase-dead control. Then test a G269T/E activation-loop variant to see whether the loop limits activity.
Hypothesis: A0A8J1IYX6 is a catalytically active protein serine/threonine kinase whose activity does not depend on activation-loop phosphorylation.
Type: in vitro kinase assay
Experiment: Determine the subcellular localization of a tagged protein in Xenopus cells, with and without the basic N-terminal region, to test cytoplasmic versus nuclear localization.
Hypothesis: The protein is mainly cytoplasmic, and its basic N-terminal region may mediate nuclear entry.
Type: localization imaging
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.
ProtNLM2 made no predictions (GO or subcellular location) for this Xenopus tropicalis protein (LOC101732819) and returned only the generic name "Protein kinase domain-containing protein". That name is correct but less specific than the gene review, which identifies an uncharacterized AGC-group protein serine/threonine kinase of PANTHER family PTHR24351 whose kinase domain is most similar to novel PKC isoforms but which lacks the C1 and C2-like regulatory domains, retains the ATP-binding lysine, HRD and DFG catalytic residues, and is inferred to act in the cytoplasm and possibly the nucleus. The gene already carries protein serine/threonine kinase activity, ATP binding, cytoplasm and nucleus in GOA, so the name adds no novel function. A PubMed search for LOC101732819, A0A8J1IYX6 and its Xenbase gene id returned no papers. With no GO or location output there is nothing to score; the absence of predictions is recorded as assessed.