NUDT2 (APAH1) encodes the human asymmetrical diadenosine tetraphosphate (Ap4A) hydrolase, a 17-kDa monomeric Nudix hydrolase that cleaves Ap4A (and related dinucleoside tetraphosphates such as Gp4G) into a nucleoside triphosphate plus a nucleoside monophosphate (ATP + AMP for Ap4A). NMR and crystal structures show a Nudix fold whose adenine-stacking binding site resembles the C. elegans orthologue and differs from plant/bacterial Ap4A hydrolases. NUDT2 is the main enzyme setting intracellular Ap4A levels: CRISPR disruption in KBM-7 cells raises Ap4A about 175-fold and broadly alters gene expression, and in immunologically activated mast cells NUDT2 degrades the Ap4A produced by lysyl-tRNA synthetase, thereby limiting Ap4A/HINT1-dependent derepression of the transcription factors MITF and USF2. The same active site also acts on RNA 5' ends: NUDT2 sequentially removes phosphates from 5'-triphosphorylated (viral) RNA, generating monophosphorylated RNA that XRN1 can degrade, and it decaps several non-canonical RNA caps in vitro (Ap4A-, FAD- and dephospho-CoA-capped RNA), with patient data implicating mRNA decapping in cellular mRNA homeostasis. NUDT2 is present in both nucleus and cytoplasm. Biallelic loss-of-function variants cause an autosomal recessive neurodevelopmental disorder with intellectual disability, motor delay and in some cases peripheral neuropathy (IDDPN). NUDT2 is overexpressed in some carcinomas and has been reported to support cancer-cell proliferation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004081 bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of asymmetrical Ap4A hydrolase activity from PANTHER node PTN000482012 (PTHR21340:SF0 animal/apicomplexan Ap4A hydrolases), seeded by pig NUDT2 (P50584), Plasmodium falciparum Ap4A hydrolase (C0H4F3) and C. elegans ndx-4. Reason: Human NUDT2 sits squarely inside the clade; the human enzyme is the classical asymmetrical Ap4A hydrolase and its loss raises cellular Ap4A dramatically. This is the defining core molecular function. Supporting Evidence: PMID:15596429 Asymmetric diadenosine 5',5'''-P(1),P(4)-tetraphosphate (Ap(4)A) hydrolases play a major role in maintaining homeostasis by cleaving the metabolite diadenosine tetraphosphate (Ap(4)A) back into ATP and AMP. PMID:27144453 causing a 175-fold increase in intracellular Ap4A |
| GO:0004081 bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated mapping from EC 3.6.1.17 / RHEA:22484 (Gp4G + H2O = GMP + GTP). Reason: Correct EC-to-GO mapping for the established core activity. Supporting Evidence: Reactome:R-HSA-5696197 Bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) (NUDT2) mediates the asymmetrical hydrolysis of P(1),P(4)-bis(5'-guanosyl) tetraphosphate (GP4G) |
| GO:0004081 bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity | ISS GO_REF:0000024 | ACCEPT | Summary: Sequence-similarity transfer from the characterised pig orthologue (P50584). Reason: Pig and human NUDT2 are near-identical orthologues; the transfer is consistent with direct evidence on the human enzyme (Ap4A accumulation on NUDT2 disruption, Ap4A-bound structures). Supporting Evidence: PMID:27144453 causing a 175-fold increase in intracellular Ap4A |
| GO:0004081 bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity | ISS PMID:11738085 Cloning, characterisation and crystallisation of a diadenosi... | ACCEPT | Summary: Similarity transfer from the biochemically characterised C. elegans ndx-4. Reason: ndx-4 is an asymmetrical Ap4A hydrolase producing AMP + ATP; the activity is conserved in the human orthologue. Supporting Evidence: PMID:11738085 It hydrolyses Ap4A with a K(m) of 7 microM and k(cat) of 27 s(-1) producing AMP and ATP as products. |
| GO:0004081 bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity | TAS Reactome:R-HSA-5696197 | ACCEPT | Summary: Reactome reaction "NUDT2 hydrolyses GP4G to GTP, GMP". Reason: Correct activity (Gp4G is an accepted substrate covered by the term definition), although the Reactome summary text internally mis-states the products as AMP and ATP. Supporting Evidence: Reactome:R-HSA-5696197 Bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) (NUDT2) mediates the asymmetrical hydrolysis of P(1),P(4)-bis(5'-guanosyl) tetraphosphate (GP4G) |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | REMOVE | Summary: High-throughput yeast two-hybrid interaction with MCM6 (HuRI precursor map). Reason: Generic protein binding from a systematic Y2H screen is uninformative about NUDT2 function and no specific activity can be derived from it; removal does not imply the interaction is false. Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: High-throughput Y2H interaction with DDIT4L (HuRI). Reason: Uninformative generic binding term from a binary interactome screen; no functional consequence established. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: High-throughput Y2H interaction with PLEKHF2 (HuRI). Reason: Uninformative generic binding term from a binary interactome screen; no functional consequence established. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome. |
| GO:0005759 mitochondrial matrix | TAS Reactome:R-HSA-5696197 | REMOVE | Summary: Compartment assigned to the Reactome reaction, which Reactome places under "Detoxification of Reactive Oxygen Species". Reason: Neither the Reactome entry nor any cited literature provides evidence for mitochondrial matrix localisation. NUDT2 has no mitochondrial targeting sequence annotated in UniProt, and immunolocalisation in human cells shows it in the nucleus and cytoplasm. The compartment appears to be an artefact of placing the reaction in a mitochondrial ROS-detoxification pathway. Supporting Evidence: PMID:34824277 In human cells, NUDT2 localizes to both the nucleus and the cytoplasm |
| GO:0006139 nucleobase-containing compound metabolic process | TAS PMID:7487923 Human diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohyd... | MODIFY | Summary: Very general process from the paper reporting the human Ap4A hydrolase cDNA and its Nudix (MutT) motif. Reason: Correct but uninformative; the specific process NUDT2 executes is Ap4A breakdown. Proposed replacements: diadenosine tetraphosphate catabolic process Supporting Evidence: PMID:7487923 This enzyme possesses a modification of the MutT sequence motif found in certain nucleotide pyrophosphatases. |
| GO:0006167 AMP biosynthetic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Process term inferred because AMP is one of the two products of Ap4A hydrolysis; the IBD on PTN000482012 is seeded only by C. elegans ndx-4 IDA rows. Reason: AMP is released as a by-product of degrading Ap4A, not as the purpose of a biosynthetic pathway, and there is no evidence that NUDT2 contributes measurably to cellular AMP pools. The worm seed annotations were themselves marked as product-based over-annotations in the ndx-4 review. The informative process is diadenosine tetraphosphate catabolic process (GO:0015967), which the node does not currently carry. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: ROLE CONFLATION Sources checked: PANTHER:PTN000482012 SUPPORTS SOURCE BUT NOT TARGET Node-level process term grounded only in the reaction product of Ap4A hydrolysis; the catabolic process term would be the appropriate node assertion. WB:WBGene00003581 Β· ndx-4 SOURCE WEAK OR INFERRED Sole seed; its own AMP biosynthetic IDA rows are product-based inferences marked over-annotated in the ndx-4 review. Supporting Evidence: PMID:15596429 cleaving the metabolite diadenosine tetraphosphate (Ap(4)A) back into ATP and AMP |
| GO:0006754 ATP biosynthetic process | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Process term inferred because ATP is a product of Ap4A hydrolysis; seeded only by ndx-4. Reason: ATP generated from micromolar Ap4A pools is negligible relative to oxidative and substrate-level phosphorylation; NUDT2 removes Ap4A rather than making ATP. Same product-based reasoning as the AMP row. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: ROLE CONFLATION Sources checked: PANTHER:PTN000482012 SUPPORTS SOURCE BUT NOT TARGET Node-level process term grounded only in the reaction product of Ap4A hydrolysis. WB:WBGene00003581 Β· ndx-4 SOURCE WEAK OR INFERRED Sole seed; its ATP biosynthetic IDA rows are product-based inferences marked over-annotated in the ndx-4 review. Supporting Evidence: PMID:15596429 cleaving the metabolite diadenosine tetraphosphate (Ap(4)A) back into ATP and AMP |
| GO:0006915 apoptotic process | ISS PMID:11937063 The crystal structure of diadenosine tetraphosphate hydrolas... | REMOVE | Summary: Similarity transfer from the C. elegans ndx-4 apoptosis TAS, which derives from a speculative sentence in the ndx-4 crystal structure paper. Reason: The source statement is hedged background ("potentially") in a structural paper, and the corresponding ndx-4 TAS was removed in the worm review. No experiment shows NUDT2 executing any step of apoptosis; NUDT2 disruption alters expression of some pro-apoptotic genes, which is an indirect transcriptional consequence of Ap4A accumulation, not participation in the apoptotic process. Supporting Evidence: PMID:11937063 Ap(4)A hydrolase has a key role in regulating the intracellular Ap(4)A levels and hence potentially the cellular response to metabolic stress and/or differentiation and apoptosis via the Ap(3)A/Ap(4)A ratio. PMID:27144453 Conversely, some pro-apoptotic genes were up-regulated. |
| GO:0008796 bis(5'-nucleosyl)-tetraphosphatase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro Tetra_PHTase (IPR003565) mapping to the parent tetraphosphatase term. Reason: Correct, broader parent of the experimentally supported asymmetrical activity (GO:0004081); an acceptable IEA. Supporting Evidence: PMID:7487923 This enzyme possesses a modification of the MutT sequence motif found in certain nucleotide pyrophosphatases. |
| GO:0008803 bis(5'-nucleosyl)-tetraphosphatase (symmetrical) activity | TAS PMID:7487923 Human diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohyd... | MODIFY | Summary: Symmetrical Ap4A hydrolase activity (Ap4A to 2 ADP) attributed to NUDT2 from the cDNA cloning paper. Reason: The essence (NUDT2 is an Ap4A hydrolase) is correct but the wrong mode of cleavage was chosen. Symmetrical (ApaH-type) Ap4A hydrolases are the prokaryotic enzymes, and the cited paper explicitly states that the human enzyme is unrelated to them; the human enzyme cleaves asymmetrically into ATP + AMP. Replace with the asymmetrical activity term. Proposed replacements: bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity Supporting Evidence: PMID:7487923 It is unrelated to the enzymes of diadenosine tetraphosphate catabolism found in prokaryotes and fungi. PMID:15596429 cleaving the metabolite diadenosine tetraphosphate (Ap(4)A) back into ATP and AMP |
| GO:0016787 hydrolase activity | IEA GO_REF:0000120 | MODIFY | Summary: Generic hydrolase activity from combined automated methods. Reason: Correct but uninformative; the specific activity is well established. Proposed replacements: bis(5'-nucleosyl)-tetraphosphatase (asymmetrical) activity Supporting Evidence: PMID:15596429 cleaving the metabolite diadenosine tetraphosphate (Ap(4)A) back into ATP and AMP |
| GO:0034599 cellular response to oxidative stress | TAS Reactome:R-HSA-3299685 | REMOVE | Summary: Derived from Reactome placing the NUDT2 Gp4G hydrolysis reaction inside "Detoxification of Reactive Oxygen Species". Reason: The Reactome pathway concerns superoxide dismutases, catalase and peroxidases; NUDT2 does not detoxify reactive oxygen species and there is no experimental evidence that it acts in an oxidative stress response. Ap4A levels rise under stress, but degrading a stress-associated nucleotide is captured by diadenosine tetraphosphate catabolic process, not by an oxidative-stress response term. Supporting Evidence: Reactome:R-HSA-3299685 Aerobic cells have defenses that detoxify reactive oxygen species by converting them to less reactive products. |
| GO:0015967 diadenosine tetraphosphate catabolic process | IMP PMID:27144453 NUDT2 Disruption Elevates Diadenosine Tetraphosphate (Ap4A) ... | NEW | Summary: Disruption of NUDT2 in human KBM-7 cells raises intracellular Ap4A 175-fold, and NUDT2 knockdown in mast cells modulates Ap4A accumulation after immunological activation. Reason: NUDT2 itself catalyses the hydrolysis of Ap4A, so it performs the catabolic step; the loss-of-function data show it is the dominant Ap4A-degrading enzyme in human cells. This is the core process and is absent from GOA for human NUDT2 (and from the PTN000482012 node). Supporting Evidence: PMID:27144453 causing a 175-fold increase in intracellular Ap4A PMID:18644867 we provided here evidence that the "Nudix" type 2 gene product, Ap(4)A hydrolase, is responsible for Ap(4)A degradation following the immunological activation of mast cells |
| GO:0140818 mRNA 5'-triphosphate monophosphatase activity | IDA PMID:34824277 NUDT2 initiates viral RNA degradation by removal of 5'-phosp... | NEW | Summary: Recombinant human NUDT2 removes the gamma-phosphate from 5'-triphosphorylated RNA and then a second phosphate, sequentially, yielding 5'-monophosphorylated RNA; the E58A Nudix-box mutant is inactive. Reason: Direct enzymatic evidence that NUDT2 releases single phosphates from 5'-PPP RNA (including PPP-RNA of HCV, which functions as mRNA). GO:0140818 describes exactly the first step (PPP-RNA to PP-RNA plus phosphate). Kept separate from the Ap4A-hydrolase function, and non-core pending evidence on cellular substrates. Supporting Evidence: PMID:34824277 Notably, NUDT2 sequentially released single phosphates resulting in a di-phosphorylated dinucleotide intermediate that is further converted into a mono-phosphorylated product PMID:34824277 NUDT2 sequentially releases two phosphates, and a monophosphorylated RNA is generated that can then serve as a substrate for the cellular exonuclease XRN1. |
| GO:0110154 RNA decapping | IMP PMID:38141063 Biallelic NUDT2 variants defective in mRNA decapping cause a... | NEW | Summary: NUDT2 decaps RNAs: patient-derived NUDT2 variants lose enzymatic activity, and add-back of a decapping-defective but Ap4A-hydrolase-competent NUDT2 implicates decapping in the altered mRNA homeostasis of NUDT2-deficient fibroblasts. In vitro NUDT2 also removes Ap4A, FAD and dpCoA caps. Reason: NUDT2 catalyses the cap cleavage itself, so it performs the step. The general RNA decapping term is used because the cellular cap types targeted are not yet resolved (in vitro activity on Ap4A-, FAD- and dpCoA-capped RNA; the Brain paper's full text was not available to establish the cap type assayed in cells). Supporting Evidence: PMID:38141063 add-back experiments using an Ap4A hydrolase defective in mRNA decapping highlighted loss of NUDT2 decapping as the activity implicated in altered mRNA homeostasis PMID:37934413 A decapping enzyme screen identifies two enzymes cleaving Ap4 A-RNA,NUDT2 and DXO PMID:32432673 Nudt2 and Nudt16 have deFADding activity in vitro. file:human/NUDT2/NUDT2-deep-research-openscientist.md NUDT2 therefore sits at the intersection of nucleotide-signaling catabolism and RNA-cap metabolism |
| GO:0005634 nucleus | IDA PMID:34824277 NUDT2 initiates viral RNA degradation by removal of 5'-phosp... | NEW | Summary: Immunolocalisation of NUDT2 in human cells shows nuclear and cytoplasmic signal. Reason: Direct localisation evidence in human cells; consistent with nuclear Ap4A signalling to MITF/USF2 via HINT1 and with nuclear localisation of the Drosophila orthologue. Supporting Evidence: PMID:34824277 In human cells, NUDT2 localizes to both the nucleus and the cytoplasm |
| GO:0005737 cytoplasm | IDA PMID:34824277 NUDT2 initiates viral RNA degradation by removal of 5'-phosp... | NEW | Summary: Immunolocalisation of NUDT2 in human cells shows nuclear and cytoplasmic signal. Reason: Direct localisation evidence in human cells. Supporting Evidence: PMID:34824277 In human cells, NUDT2 localizes to both the nucleus and the cytoplasm |
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Download this section (compressed HTML)Q: Which NUDT2 activity is physiologically dominant in neurons: Ap4A hydrolysis or RNA 5'-end processing/decapping, and which cap types (m7G, Ap4A, FAD, dpCoA) are the relevant cellular substrates?
Q: Should the PANTHER node PTN000482012 carry diadenosine tetraphosphate catabolic process (GO:0015967) in place of the product-based AMP/ATP biosynthetic process IBDs seeded only by C. elegans ndx-4?
Q: Is there a GO molecular function term for sequential dephosphorylation of 5'-PPP RNA that is not restricted to mRNA (viral genomic RNA), or should GO:0140818 be broadened?
Q: Does NUDT2 positively regulate mTORC1 via Rag GTPase binding independently of its catalytic activity?
Experiment: In patient-derived neurons or iPSC neural lineages, separate Ap4A-hydrolase and decapping roles using separation-of-function NUDT2 alleles, combined with cap-seq (CapQ/LC-MS) and Ap4A quantification.
Experiment: Profile Ap4A-capped, FAD-capped and dpCoA-capped RNAs transcriptome-wide in NUDT2 knockout versus rescued cells under stress conditions that elevate Ap4A.
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