{"gene":"PRPS1","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2023,"finding":"Human PRPS1 assembles into filaments in both active and inhibited states, with conserved assembly interfaces that stabilize the binding site for the essential activator phosphate, thereby increasing enzymatic activity. Structures also revealed coupling of catalysis in one active site with product release in an adjacent site, demonstrating an additional allosteric regulatory layer provided by filament formation. Some disease-associated mutations alter filament assembly, linking filament stability to activity.","method":"Cryo-EM structure determination of active and inhibited PRPS1 filaments, combined with mutagenesis of disease variants","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures in multiple states with functional mutagenesis validation","pmids":["36747094"],"is_preprint":false},{"year":1993,"finding":"Point mutations in PRPS1 (N113S and D182H) confer purine nucleotide feedback resistance and enzyme superactivity. Recombinant mutant PRS1 proteins expressed in E. coli reproduced the feedback-resistant phenotype seen in patient cells, establishing these specific residues as critical for allosteric inhibition by ADP/GDP.","method":"PCR sequencing of patient cDNA, RNase mapping, and expression of recombinant wild-type and mutant PRPS1 in E. coli with enzymatic assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis confirming feedback-resistance mechanism","pmids":["8253776"],"is_preprint":false},{"year":2007,"finding":"Loss-of-function missense mutations in PRPS1 (L152P and Q133P) cause Arts syndrome by abolishing phosphoribosyl pyrophosphate synthetase 1 enzymatic activity, leading to impaired purine biosynthesis as evidenced by undetectable hypoxanthine in urine and reduced uric acid in serum.","method":"Molecular modeling in silico plus enzymatic activity assays in erythrocytes and fibroblasts from patients","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro enzymatic assay in patient-derived cells plus structural modeling; replicated across two families","pmids":["17701896"],"is_preprint":false},{"year":2007,"finding":"Missense mutations in PRPS1 (E43D and M115T) at conserved residues cause X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) with decreased PRPS1 enzymatic activity demonstrated in patients harboring the M115T mutation.","method":"Mutation identification by sequencing, enzymatic activity assay in patient samples","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — direct enzymatic activity measurement in patient-derived material with segregation analysis","pmids":["17701900"],"is_preprint":false},{"year":2010,"finding":"Loss-of-function missense mutations in PRPS1 cause DFN2 nonsyndromic X-linked sensorineural deafness by abolishing PRPP synthetase 1 activity, confirmed by structural analysis and enzymatic activity assays in erythrocytes and fibroblasts; Prps1 is expressed in murine cochlear and vestibular hair cells and spiral ganglion postnatally.","method":"Structural analysis in silico, enzymatic activity assays in patient erythrocytes and fibroblasts, in situ hybridization in mouse cochlea","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — enzymatic assay replicated in two cell types plus localization by in situ hybridization","pmids":["20021999"],"is_preprint":false},{"year":1999,"finding":"PRS superactivity in certain patients results from accelerated PRPS1 transcription (3–4-fold increase) rather than gene amplification or mRNA stabilization, and increased PRPS1 transcription is a major determinant of PRPP and purine nucleotide synthesis rates.","method":"Northern blot, slot blotting of nuclear run-offs, Southern blot in patient fibroblasts and lymphoblasts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal transcriptional assays identifying accelerated transcription as mechanism","pmids":["10066814"],"is_preprint":false},{"year":2015,"finding":"Relapse-specific gain-of-function missense mutations in PRPS1 reduce feedback inhibition by ADP/GDP (negative feedback-defective), constitutively activating de novo purine biosynthesis and competitively inhibiting thiopurine activation, thereby causing thiopurine resistance in childhood ALL. The de novo purine synthesis inhibitor lometrexol abrogates this resistance.","method":"Whole-exome sequencing of relapsed ALL samples, functional expression of PRPS1 mutants, enzymatic feedback inhibition assays, drug resistance assays in cell lines and xenograft models","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1–2 — enzymatic assay plus cell-based functional validation plus in vivo rescue; highly cited foundational study","pmids":["25962120"],"is_preprint":false},{"year":2019,"finding":"CDK1 phosphorylates PRPS1 at serine 103 during S phase, upregulating its enzymatic activity to fuel nucleotide synthesis for DNA replication. Loss of S103 phosphorylation delays cell cycle progression and decreases colorectal cancer cell proliferation.","method":"Cell-cycle synchronization assays, site-directed mutagenesis (S103A), enzymatic activity assays, phospho-specific antibody staining in 184 colorectal cancer tissue samples","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis coupled with enzymatic activity measurement and cell-cycle phenotype readout, validated in patient tissues","pmids":["31253668"],"is_preprint":false},{"year":2015,"finding":"miR-124 directly targets PRPS1 mRNA (and RPIA mRNA), reducing PRPS1 protein levels and thereby decreasing glucose consumption, ATP levels, DNA synthesis, and proliferation in colorectal cancer cells. Overexpression of PRPS1 rescues glycometabolism in miR-124-expressing cells.","method":"cDNA microarray, luciferase reporter (target validation), siRNA knockdown, lentiviral overexpression, xenograft tumor model","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 — direct target validation with reporter assay plus rescue experiment plus in vivo xenograft","pmids":["26248089"],"is_preprint":false},{"year":2018,"finding":"PRPS1 feedback-defective mutations increase intracellular PRPP levels, which promote conversion of 5-FU to FUMP and FUTP, enhancing 5-FU-induced DNA damage and apoptosis in ALL cells, providing a mechanism for selective 5-FU sensitivity of PRPS1 mutant cells.","method":"Drug sensitivity assays in PRPS1 mutant vs. control ALL cell lines, PRPP level measurement, metabolite analysis of 5-FU conversion, apoptosis/DNA damage assays","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — metabolic and functional assays in isogenic cell lines, single lab","pmids":["30255549"],"is_preprint":false},{"year":2022,"finding":"PRPS2 mutations in relapsed ALL destabilize the PRPS1/2 hexamer, reducing nucleotide feedback inhibition and enhancing thiopurine resistance. The 3-amino-acid insert (V103-G104-E105) in PRPS2 causes steric clash at the hexamer interface, explaining the low baseline activity of PRPS2 relative to PRPS1.","method":"Ultra-deep sequencing, in vitro PRPS enzyme activity assay, ADP/GDP feedback inhibition assay, UPLC-MS/MS metabolite analysis, xenograft models","journal":"Blood science","confidence":"High","confidence_rationale":"Tier 1–2 — enzymatic assay, structural reasoning, metabolomics, and in vivo validation","pmids":["36742181"],"is_preprint":false},{"year":2017,"finding":"A gain-of-function PRPS1 mutation (L191F) affects the architecture of both allosteric inhibitory sites in the crystal structure of human PRPP synthetase, preventing allosteric feedback inhibition and causing enzyme superactivity with uric acid overproduction.","method":"Crystal structure analysis of human PRPS1 with mutant modeling, enzyme activity confirmation","journal":"American journal of medical genetics. Part A","confidence":"Medium","confidence_rationale":"Tier 2 — structural analysis combined with enzymatic activity confirmation in single study","pmids":["28742244"],"is_preprint":false},{"year":2021,"finding":"PRPS1 knockout causes DNA damage and apoptosis in pluripotent stem cells (PSCs), establishing PRPS1-mediated purine biosynthesis as essential for PSC survival, while PRPS2 depletion attenuates stemness and promotes differentiation.","method":"PRPS1 knockout in PSCs, UHPLC-MS metabolite analysis, apoptosis and DNA damage assays","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with defined cellular phenotype plus metabolite profiling, single lab","pmids":["33493137"],"is_preprint":false},{"year":2016,"finding":"Knockdown of PRPS1 in zebrafish (prps1a and prps1b) results in smaller otic vesicles, reduced inner ear hair cell numbers, abnormal primary motor neuron development, and reduced leukocytes, phenocopying human deafness and Arts syndrome features; double mutants show increasingly severe phenotypes associated with prolonged cell cycle from reduced nucleotide synthesis.","method":"Zebrafish CRISPR/morpholino knockdown, confocal imaging, hair cell counting, primary motor neuron analysis, cell cycle analysis","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in vertebrate model with multiple orthogonal phenotypic readouts, replicated across allele combinations","pmids":["27425195"],"is_preprint":false},{"year":2025,"finding":"PRPS1 deficiency in HEI-OC1 cells causes downregulation of the NAD+/SIRT3/SOD2 pathway, increased reactive oxygen species accumulation, mitochondrial dysfunction, and apoptosis; these defects are partially rescued by nicotinamide mononucleotide (NMN) supplementation. In zebrafish, overexpression of mutant PRPS1 (p.Cys165Tyr) leads to hair cell death and disrupted swimming behavior.","method":"siRNA knockdown in HEI-OC1 cells, ROS measurement, mitochondrial function assays, NAD+/SIRT3/SOD2 pathway analysis, zebrafish transgenic overexpression model","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with pathway analysis and rescue experiment in two model systems, single lab","pmids":["40677922"],"is_preprint":false},{"year":2025,"finding":"AMPK phosphorylates PRPS1, suppressing its activity; NDUFS3-mediated promotion of OXPHOS and PPP increases ATP, inhibiting AMPK, which in turn releases PRPS1 from inhibitory phosphorylation and enhances purine nucleotide biosynthesis to drive melanoma proliferation.","method":"NDUFS3 knockdown/overexpression, AMPK activity assays, PRPS1 phosphorylation detection, metabolic flux analysis in melanoma cells","journal":"Cell death and differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — kinase-substrate relationship established by functional assays in cell lines, single lab","pmids":["40404919"],"is_preprint":false},{"year":2025,"finding":"EGF-activated CK2 phosphorylates the circadian protein CLOCK at S106, causing its nuclear export; cytosolic CLOCK then acetylates PRPS1 (and PRPS2) at K29, protecting them from HSC70-mediated degradation and enhancing GBM cell proliferation and migration.","method":"Site-directed mutagenesis, immunoprecipitation, immunofluorescence, subcellular fractionation, shRNA silencing, IHC in GBM specimens","journal":"Journal of neuro-oncology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing writer (CLOCK), modification site (K29ac), and functional consequence, single lab","pmids":["40682742"],"is_preprint":false},{"year":1992,"finding":"The PRPS1 promoter contains a TATA-like sequence, CCAAT box, and three Sp1 binding sites, and a 2.0 kb 5'-flanking region drives reporter gene (CAT) expression with activity correlating with endogenous PRPS1 mRNA levels across cell lines, establishing these cis-elements as functional promoter elements.","method":"CAT/promoter fusion reporter assay in four cell lines, S1 nuclease and primer extension mapping of transcription start sites","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — functional reporter assay identifying active promoter elements","pmids":["1314091"],"is_preprint":false},{"year":2022,"finding":"NRF2 functions as an upstream transcription factor of PRPS1, driving its upregulation in melanoma; increased PRPS1 promotes melanoma cell proliferation, migration, invasion, and inhibits apoptosis both in vitro and in vivo.","method":"ChIP or transcription factor binding assay (NRF2-PRPS1), knockdown/overexpression in melanoma cell lines, xenograft tumor models","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 3 — transcription factor–target relationship established, functional phenotype shown, single lab","pmids":["36203561"],"is_preprint":false},{"year":2021,"finding":"SAM supplementation replenishes erythrocyte purine nucleotides (adenosine and guanosine) in an Arts syndrome (PRPS1 deficiency) patient; co-therapy with SAM and nicotinamide riboside further improved T-cell survival and function, supporting the role of PRPS1 in purine and NAD+ nucleotide supply in immune cells.","method":"Clinical supplementation trial with biochemical monitoring of erythrocyte nucleotide levels and T-cell functional assays","journal":"Molecular genetics and metabolism reports","confidence":"Medium","confidence_rationale":"Tier 3 — functional rescue in a single patient with biochemical endpoint measurement","pmids":["33532242"],"is_preprint":false},{"year":2024,"finding":"The mammalian PRPS enzyme complex comprises three isozymes (PRPS1, PRPS2, testis-restricted PRPS3) and two non-enzymatic associated proteins (PRPSAP1, PRPSAP2) that operate together as a large molecular weight complex with heterogeneous multimeric configurations; cells lacking PRPS2, PRPSAP1, and PRPSAP2 render PRPS1 into aberrant homo-oligomeric assemblies with diminished metabolic flux and impaired proliferative capacity.","method":"Isogenic fibroblast knockout clones in combinatorial assembly states, co-immunoprecipitation, metabolic flux analysis, proliferation assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods in isogenic cell panel, preprint not yet peer-reviewed","pmids":["bio_10.1101_2024.10.01.616059"],"is_preprint":true}],"current_model":"PRPS1 encodes phosphoribosyl pyrophosphate synthetase 1, a rate-limiting enzyme that phosphorylates ribose-5-phosphate to produce PRPP (the central precursor for de novo and salvage purine, pyrimidine, and pyridine nucleotide biosynthesis); its activity is allosterically inhibited by ADP/GDP and activated by inorganic phosphate, with filament assembly stabilizing the phosphate-binding site to provide an additional regulatory layer; disease mutations either abolish this feedback inhibition (superactivity/thiopurine resistance) or reduce catalytic activity (deafness, neuropathy, Arts syndrome); cell-cycle-dependent CDK1 phosphorylation at S103, AMPK-mediated inhibitory phosphorylation, and CLOCK-mediated K29 acetylation further tune PRPS1 activity to couple nucleotide supply to proliferative demand."},"narrative":{"teleology":[{"year":1992,"claim":"Defining the transcriptional architecture of PRPS1 established how its housekeeping expression is controlled, revealing a TATA-like element, CCAAT box, and Sp1 sites as functional cis-regulatory elements.","evidence":"CAT reporter assay with 2.0 kb 5'-flanking region across four cell lines, with S1 nuclease/primer extension mapping","pmids":["1314091"],"confidence":"Medium","gaps":["Identity of cell-type-specific trans-acting factors beyond Sp1 not resolved","Chromatin context not examined"]},{"year":1993,"claim":"Identification of N113S and D182H as feedback-resistance mutations established the molecular basis for allosteric inhibition of PRPS1 by purine nucleotides, answering how the enzyme is regulated at the product level.","evidence":"Recombinant mutant PRPS1 expressed in E. coli with in vitro enzymatic assay showing loss of ADP/GDP inhibition","pmids":["8253776"],"confidence":"High","gaps":["Structural basis of allosteric sites not yet resolved at this time","Whether additional residues participate in feedback not tested"]},{"year":1999,"claim":"Discovery that some PRPS1 superactivity results from accelerated transcription rather than coding mutations revealed a second disease mechanism and demonstrated that transcriptional output is rate-limiting for PRPP production.","evidence":"Northern blot, nuclear run-on, and Southern blot in patient fibroblasts/lymphoblasts","pmids":["10066814"],"confidence":"High","gaps":["Transcription factor(s) driving increased transcription not identified","Epigenetic contribution not examined"]},{"year":2007,"claim":"Loss-of-function mutations were shown to cause two distinct X-linked diseases—Arts syndrome (L152P, Q133P) and CMTX5 neuropathy (E43D, M115T)—establishing that reduced PRPS1 activity impairs purine supply in neurons and immune cells.","evidence":"Enzymatic activity assays in patient erythrocytes and fibroblasts, segregation analysis in families","pmids":["17701896","17701900"],"confidence":"High","gaps":["Cell-type-specific vulnerability (why neurons and hair cells are selectively affected) not explained","No animal model validation at this stage"]},{"year":2010,"claim":"Linking additional loss-of-function PRPS1 mutations to X-linked nonsyndromic deafness (DFN2) and demonstrating cochlear expression established that auditory hair cells are critically dependent on PRPS1-mediated nucleotide synthesis.","evidence":"Enzymatic assays in patient cells plus in situ hybridization of Prps1 in mouse cochlea","pmids":["20021999"],"confidence":"High","gaps":["Whether cochlear phenotype is purine-specific or involves pyrimidine/NAD+ depletion not resolved","No conditional knockout in inner ear"]},{"year":2015,"claim":"Relapse-specific gain-of-function PRPS1 mutations were identified as a major mechanism of thiopurine resistance in childhood ALL, showing that loss of feedback inhibition constitutively activates de novo purine synthesis and competitively blocks thiopurine activation.","evidence":"Whole-exome sequencing of relapsed ALL, in vitro feedback inhibition assays, cell line drug resistance assays, and xenograft models","pmids":["25962120"],"confidence":"High","gaps":["Frequency and clonal dynamics of PRPS1 mutations across ALL subtypes not fully mapped","Structural mechanism of how mutations alter allosteric sites not yet visualized"]},{"year":2015,"claim":"Identification of miR-124 as a direct negative regulator of PRPS1 mRNA demonstrated a post-transcriptional control layer linking metabolic reprogramming to colorectal cancer proliferation.","evidence":"Luciferase reporter target validation, siRNA/overexpression rescue, xenograft tumor model","pmids":["26248089"],"confidence":"High","gaps":["Extent to which miR-124 regulation operates in non-malignant tissues not assessed","Other miRNAs targeting PRPS1 not surveyed"]},{"year":2016,"claim":"Zebrafish PRPS1 knockdown phenocopied human deafness and Arts syndrome features—smaller otic vesicles, reduced hair cells, motor neuron defects, and immune cell loss—providing the first vertebrate genetic model and linking the phenotype to prolonged cell cycle from nucleotide insufficiency.","evidence":"CRISPR/morpholino knockdown in zebrafish with confocal imaging, hair cell counting, and cell cycle analysis","pmids":["27425195"],"confidence":"High","gaps":["Mammalian conditional knockout not yet performed","Contribution of pyrimidine vs. purine depletion not separated"]},{"year":2017,"claim":"The crystal structure of PRPS1 with the L191F superactivity mutation revealed how a single residue change disrupts both allosteric inhibitory sites, providing the first atomic-resolution explanation for feedback-resistant enzyme superactivity.","evidence":"X-ray crystal structure of human PRPS1 with mutant modeling and enzymatic confirmation","pmids":["28742244"],"confidence":"Medium","gaps":["Only one superactivity mutation structurally characterized","Structure of full inhibited state not captured"]},{"year":2019,"claim":"CDK1-mediated phosphorylation of PRPS1 at S103 during S phase established a direct cell-cycle-dependent mechanism for upregulating nucleotide production during DNA replication, linking PRPS1 to proliferative control in colorectal cancer.","evidence":"Cell-cycle synchronization, S103A mutagenesis, enzymatic activity assays, phospho-specific antibody staining in 184 colorectal cancer tissues","pmids":["31253668"],"confidence":"High","gaps":["Whether other CDK substrates in the PRPS complex are co-regulated not examined","Phosphatase responsible for S103 dephosphorylation not identified"]},{"year":2021,"claim":"PRPS1 knockout in pluripotent stem cells caused DNA damage and apoptosis, demonstrating that PRPS1-dependent purine biosynthesis is essential for stem cell genome integrity and survival.","evidence":"PRPS1 knockout in PSCs with UHPLC-MS metabolite profiling, apoptosis, and DNA damage assays","pmids":["33493137"],"confidence":"Medium","gaps":["Whether PRPS2 can compensate in other stem cell contexts not tested","Downstream nucleotide species responsible for DNA damage not pinpointed"]},{"year":2022,"claim":"NRF2 was identified as an upstream transcriptional activator of PRPS1 in melanoma, providing a mechanism by which oxidative stress signaling rewires nucleotide metabolism to support tumor growth.","evidence":"ChIP/transcription factor binding assay, knockdown/overexpression in melanoma lines, xenograft models","pmids":["36203561"],"confidence":"Medium","gaps":["Direct NRF2 binding site in PRPS1 promoter not mapped at nucleotide resolution","Not confirmed in non-melanoma contexts"]},{"year":2022,"claim":"PRPS2 mutations in relapsed ALL were shown to destabilize the PRPS1/2 hexamer interface and reduce nucleotide feedback inhibition, demonstrating that the hetero-oligomeric context of PRPS1 is critical for proper allosteric regulation.","evidence":"Ultra-deep sequencing, in vitro enzyme assays, ADP/GDP feedback inhibition assays, UPLC-MS/MS metabolomics, xenograft models","pmids":["36742181"],"confidence":"High","gaps":["Stoichiometry of PRPS1:PRPS2 in normal vs. leukemic cells not determined","Whether PRPSAP1/AP2 modulate this phenotype not addressed"]},{"year":2023,"claim":"Cryo-EM structures of PRPS1 filaments in active and inhibited states revealed that polymerization stabilizes the phosphate-binding site and couples catalysis with product release across adjacent active sites, establishing filament assembly as a fundamental regulatory mechanism.","evidence":"Cryo-EM structure determination of filaments in multiple states with disease-variant mutagenesis","pmids":["36747094"],"confidence":"High","gaps":["In vivo evidence for filament formation not yet obtained","How filament assembly/disassembly is regulated by cellular signals is unknown"]},{"year":2025,"claim":"AMPK-mediated inhibitory phosphorylation of PRPS1 established a direct energy-sensing mechanism that suppresses nucleotide biosynthesis under metabolic stress, linking OXPHOS status to PRPS1 output in melanoma.","evidence":"NDUFS3 knockdown/overexpression, AMPK activity assays, PRPS1 phosphorylation detection, metabolic flux analysis in melanoma cells","pmids":["40404919"],"confidence":"Medium","gaps":["Specific AMPK phosphorylation site(s) on PRPS1 not mapped","Not confirmed in non-melanoma cell types"]},{"year":2025,"claim":"CLOCK-mediated K29 acetylation of PRPS1 was shown to protect it from HSC70-dependent degradation, revealing a circadian/signaling-dependent post-translational stabilization mechanism relevant to glioblastoma proliferation.","evidence":"Site-directed mutagenesis, immunoprecipitation, immunofluorescence, subcellular fractionation, shRNA silencing in GBM cells","pmids":["40682742"],"confidence":"Medium","gaps":["Deacetylase(s) that reverse K29 acetylation not identified","Circadian oscillation of PRPS1 protein levels not directly demonstrated"]},{"year":2025,"claim":"PRPS1 deficiency was linked to NAD+/SIRT3/SOD2 pathway downregulation and mitochondrial dysfunction in auditory cells, providing a mechanistic explanation for hair cell vulnerability in PRPS1-associated deafness and suggesting NAD+ precursor supplementation as a rescue strategy.","evidence":"siRNA knockdown in HEI-OC1 cells with ROS/mitochondrial assays and NMN rescue; zebrafish mutant PRPS1 overexpression model","pmids":["40677922"],"confidence":"Medium","gaps":["Whether NAD+ depletion or purine depletion is the primary cause of hair cell death not fully dissected","NMN rescue only partial; in vivo mammalian validation lacking"]},{"year":null,"claim":"Key unresolved questions include: how PRPS1 filament assembly and disassembly are regulated in vivo; what determines cell-type-specific vulnerability to PRPS1 deficiency (neurons, hair cells, immune cells); and the precise stoichiometry and regulatory roles of PRPSAP1/PRPSAP2 within the native PRPS complex.","evidence":"","pmids":[],"confidence":"High","gaps":["No in vivo evidence for filament dynamics","Conditional tissue-specific knockout in mammals not performed","Native complex stoichiometry and its regulation remain poorly defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,6,7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,11]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7,16]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,2,6,7,9,12]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[7,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,9]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[7]}],"complexes":["PRPS hexamer (PRPS1/PRPS2/PRPSAP1/PRPSAP2)","PRPS1 filament"],"partners":["PRPS2","PRPSAP1","PRPSAP2","CDK1","AMPK","CLOCK","HSC70","NRF2"],"other_free_text":[]},"mechanistic_narrative":"PRPS1 encodes phosphoribosyl pyrophosphate synthetase 1, the rate-limiting enzyme that converts ribose-5-phosphate to PRPP, the universal precursor for de novo and salvage synthesis of purine, pyrimidine, and NAD+ nucleotides, thereby coupling nucleotide supply to cell proliferation, DNA replication, and tissue maintenance. The enzyme is allosterically inhibited by ADP and GDP at two distinct sites, and gain-of-function mutations that disrupt this feedback cause enzyme superactivity with uric acid overproduction and thiopurine resistance in relapsed ALL, while loss-of-function mutations cause Arts syndrome, CMTX5 neuropathy, and X-linked nonsyndromic deafness (DFN2) [PMID:8253776, PMID:25962120, PMID:17701896, PMID:17701900, PMID:20021999]. PRPS1 assembles into filaments in both active and inhibited conformations; filament interfaces stabilize the phosphate-binding site to enhance catalytic activity, and disease-associated mutations alter filament assembly [PMID:36747094]. Activity is further tuned by CDK1 phosphorylation at S103 during S phase to fuel DNA replication, by AMPK-mediated inhibitory phosphorylation linking energy status to nucleotide output, and by CLOCK-mediated K29 acetylation that protects PRPS1 from HSC70-dependent degradation [PMID:31253668, PMID:40404919, PMID:40682742]."},"prefetch_data":{"uniprot":{"accession":"P60891","full_name":"Ribose-phosphate pyrophosphokinase 1","aliases":["PPRibP","Phosphoribosyl pyrophosphate synthase I","PRS-I"],"length_aa":318,"mass_kda":34.8,"function":"Catalyzes the synthesis of phosphoribosylpyrophosphate (PRPP) that is essential for nucleotide synthesis","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/P60891/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PRPS1","classification":"Not Classified","n_dependent_lines":12,"n_total_lines":1208,"dependency_fraction":0.009933774834437087},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CAPZB","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PRPS1","total_profiled":1310},"omim":[{"mim_id":"611566","title":"PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE 1-LIKE 1; PRPS1L1","url":"https://www.omim.org/entry/611566"},{"mim_id":"610960","title":"MICRO RNA 376A2; MIR376A2","url":"https://www.omim.org/entry/610960"},{"mim_id":"610959","title":"MICRO RNA 376A1; MIR376A1","url":"https://www.omim.org/entry/610959"},{"mim_id":"603762","title":"PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE-ASSOCIATED PROTEIN 2; PRPSAP2","url":"https://www.omim.org/entry/603762"},{"mim_id":"601249","title":"PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE-ASSOCIATED PROTEIN 1; PRPSAP1","url":"https://www.omim.org/entry/601249"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PRPS1"},"hgnc":{"alias_symbol":["CMTX5","DFNX1","PRS-I","PPRibP"],"prev_symbol":["DFN2"]},"alphafold":{"accession":"P60891","domains":[{"cath_id":"3.40.50.2020","chopping":"3-145","consensus_level":"high","plddt":96.526,"start":3,"end":145},{"cath_id":"3.40.50.2020","chopping":"147-195_205-290","consensus_level":"high","plddt":96.2906,"start":147,"end":290}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P60891","model_url":"https://alphafold.ebi.ac.uk/files/AF-P60891-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P60891-F1-predicted_aligned_error_v6.png","plddt_mean":94.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PRPS1","jax_strain_url":"https://www.jax.org/strain/search?query=PRPS1"},"sequence":{"accession":"P60891","fasta_url":"https://rest.uniprot.org/uniprotkb/P60891.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P60891/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P60891"}},"corpus_meta":[{"pmid":"25962120","id":"PMC_25962120","title":"Negative feedback-defective PRPS1 mutants drive thiopurine resistance in relapsed childhood ALL.","date":"2015","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/25962120","citation_count":135,"is_preprint":false},{"pmid":"20380929","id":"PMC_20380929","title":"PRPS1 mutations: four distinct syndromes and potential treatment.","date":"2010","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20380929","citation_count":97,"is_preprint":false},{"pmid":"17701900","id":"PMC_17701900","title":"Mutations in PRPS1, which encodes the phosphoribosyl pyrophosphate synthetase enzyme critical for nucleotide biosynthesis, cause hereditary peripheral neuropathy with hearing loss and optic neuropathy (cmtx5).","date":"2007","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17701900","citation_count":95,"is_preprint":false},{"pmid":"20021999","id":"PMC_20021999","title":"Loss-of-function mutations in the PRPS1 gene cause a type 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states, with conserved assembly interfaces that stabilize the binding site for the essential activator phosphate, thereby increasing enzymatic activity. Structures also revealed coupling of catalysis in one active site with product release in an adjacent site, demonstrating an additional allosteric regulatory layer provided by filament formation. Some disease-associated mutations alter filament assembly, linking filament stability to activity.\",\n      \"method\": \"Cryo-EM structure determination of active and inhibited PRPS1 filaments, combined with mutagenesis of disease variants\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures in multiple states with functional mutagenesis validation\",\n      \"pmids\": [\"36747094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Point mutations in PRPS1 (N113S and D182H) confer purine nucleotide feedback resistance and enzyme superactivity. Recombinant mutant PRS1 proteins expressed in E. coli reproduced the feedback-resistant phenotype seen in patient cells, establishing these specific residues as critical for allosteric inhibition by ADP/GDP.\",\n      \"method\": \"PCR sequencing of patient cDNA, RNase mapping, and expression of recombinant wild-type and mutant PRPS1 in E. coli with enzymatic assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis confirming feedback-resistance mechanism\",\n      \"pmids\": [\"8253776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Loss-of-function missense mutations in PRPS1 (L152P and Q133P) cause Arts syndrome by abolishing phosphoribosyl pyrophosphate synthetase 1 enzymatic activity, leading to impaired purine biosynthesis as evidenced by undetectable hypoxanthine in urine and reduced uric acid in serum.\",\n      \"method\": \"Molecular modeling in silico plus enzymatic activity assays in erythrocytes and fibroblasts from patients\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro enzymatic assay in patient-derived cells plus structural modeling; replicated across two families\",\n      \"pmids\": [\"17701896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Missense mutations in PRPS1 (E43D and M115T) at conserved residues cause X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) with decreased PRPS1 enzymatic activity demonstrated in patients harboring the M115T mutation.\",\n      \"method\": \"Mutation identification by sequencing, enzymatic activity assay in patient samples\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct enzymatic activity measurement in patient-derived material with segregation analysis\",\n      \"pmids\": [\"17701900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Loss-of-function missense mutations in PRPS1 cause DFN2 nonsyndromic X-linked sensorineural deafness by abolishing PRPP synthetase 1 activity, confirmed by structural analysis and enzymatic activity assays in erythrocytes and fibroblasts; Prps1 is expressed in murine cochlear and vestibular hair cells and spiral ganglion postnatally.\",\n      \"method\": \"Structural analysis in silico, enzymatic activity assays in patient erythrocytes and fibroblasts, in situ hybridization in mouse cochlea\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — enzymatic assay replicated in two cell types plus localization by in situ hybridization\",\n      \"pmids\": [\"20021999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PRS superactivity in certain patients results from accelerated PRPS1 transcription (3–4-fold increase) rather than gene amplification or mRNA stabilization, and increased PRPS1 transcription is a major determinant of PRPP and purine nucleotide synthesis rates.\",\n      \"method\": \"Northern blot, slot blotting of nuclear run-offs, Southern blot in patient fibroblasts and lymphoblasts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal transcriptional assays identifying accelerated transcription as mechanism\",\n      \"pmids\": [\"10066814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Relapse-specific gain-of-function missense mutations in PRPS1 reduce feedback inhibition by ADP/GDP (negative feedback-defective), constitutively activating de novo purine biosynthesis and competitively inhibiting thiopurine activation, thereby causing thiopurine resistance in childhood ALL. The de novo purine synthesis inhibitor lometrexol abrogates this resistance.\",\n      \"method\": \"Whole-exome sequencing of relapsed ALL samples, functional expression of PRPS1 mutants, enzymatic feedback inhibition assays, drug resistance assays in cell lines and xenograft models\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — enzymatic assay plus cell-based functional validation plus in vivo rescue; highly cited foundational study\",\n      \"pmids\": [\"25962120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CDK1 phosphorylates PRPS1 at serine 103 during S phase, upregulating its enzymatic activity to fuel nucleotide synthesis for DNA replication. Loss of S103 phosphorylation delays cell cycle progression and decreases colorectal cancer cell proliferation.\",\n      \"method\": \"Cell-cycle synchronization assays, site-directed mutagenesis (S103A), enzymatic activity assays, phospho-specific antibody staining in 184 colorectal cancer tissue samples\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis coupled with enzymatic activity measurement and cell-cycle phenotype readout, validated in patient tissues\",\n      \"pmids\": [\"31253668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"miR-124 directly targets PRPS1 mRNA (and RPIA mRNA), reducing PRPS1 protein levels and thereby decreasing glucose consumption, ATP levels, DNA synthesis, and proliferation in colorectal cancer cells. Overexpression of PRPS1 rescues glycometabolism in miR-124-expressing cells.\",\n      \"method\": \"cDNA microarray, luciferase reporter (target validation), siRNA knockdown, lentiviral overexpression, xenograft tumor model\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct target validation with reporter assay plus rescue experiment plus in vivo xenograft\",\n      \"pmids\": [\"26248089\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PRPS1 feedback-defective mutations increase intracellular PRPP levels, which promote conversion of 5-FU to FUMP and FUTP, enhancing 5-FU-induced DNA damage and apoptosis in ALL cells, providing a mechanism for selective 5-FU sensitivity of PRPS1 mutant cells.\",\n      \"method\": \"Drug sensitivity assays in PRPS1 mutant vs. control ALL cell lines, PRPP level measurement, metabolite analysis of 5-FU conversion, apoptosis/DNA damage assays\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — metabolic and functional assays in isogenic cell lines, single lab\",\n      \"pmids\": [\"30255549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PRPS2 mutations in relapsed ALL destabilize the PRPS1/2 hexamer, reducing nucleotide feedback inhibition and enhancing thiopurine resistance. The 3-amino-acid insert (V103-G104-E105) in PRPS2 causes steric clash at the hexamer interface, explaining the low baseline activity of PRPS2 relative to PRPS1.\",\n      \"method\": \"Ultra-deep sequencing, in vitro PRPS enzyme activity assay, ADP/GDP feedback inhibition assay, UPLC-MS/MS metabolite analysis, xenograft models\",\n      \"journal\": \"Blood science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — enzymatic assay, structural reasoning, metabolomics, and in vivo validation\",\n      \"pmids\": [\"36742181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A gain-of-function PRPS1 mutation (L191F) affects the architecture of both allosteric inhibitory sites in the crystal structure of human PRPP synthetase, preventing allosteric feedback inhibition and causing enzyme superactivity with uric acid overproduction.\",\n      \"method\": \"Crystal structure analysis of human PRPS1 with mutant modeling, enzyme activity confirmation\",\n      \"journal\": \"American journal of medical genetics. Part A\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — structural analysis combined with enzymatic activity confirmation in single study\",\n      \"pmids\": [\"28742244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PRPS1 knockout causes DNA damage and apoptosis in pluripotent stem cells (PSCs), establishing PRPS1-mediated purine biosynthesis as essential for PSC survival, while PRPS2 depletion attenuates stemness and promotes differentiation.\",\n      \"method\": \"PRPS1 knockout in PSCs, UHPLC-MS metabolite analysis, apoptosis and DNA damage assays\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined cellular phenotype plus metabolite profiling, single lab\",\n      \"pmids\": [\"33493137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Knockdown of PRPS1 in zebrafish (prps1a and prps1b) results in smaller otic vesicles, reduced inner ear hair cell numbers, abnormal primary motor neuron development, and reduced leukocytes, phenocopying human deafness and Arts syndrome features; double mutants show increasingly severe phenotypes associated with prolonged cell cycle from reduced nucleotide synthesis.\",\n      \"method\": \"Zebrafish CRISPR/morpholino knockdown, confocal imaging, hair cell counting, primary motor neuron analysis, cell cycle analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in vertebrate model with multiple orthogonal phenotypic readouts, replicated across allele combinations\",\n      \"pmids\": [\"27425195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PRPS1 deficiency in HEI-OC1 cells causes downregulation of the NAD+/SIRT3/SOD2 pathway, increased reactive oxygen species accumulation, mitochondrial dysfunction, and apoptosis; these defects are partially rescued by nicotinamide mononucleotide (NMN) supplementation. In zebrafish, overexpression of mutant PRPS1 (p.Cys165Tyr) leads to hair cell death and disrupted swimming behavior.\",\n      \"method\": \"siRNA knockdown in HEI-OC1 cells, ROS measurement, mitochondrial function assays, NAD+/SIRT3/SOD2 pathway analysis, zebrafish transgenic overexpression model\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with pathway analysis and rescue experiment in two model systems, single lab\",\n      \"pmids\": [\"40677922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AMPK phosphorylates PRPS1, suppressing its activity; NDUFS3-mediated promotion of OXPHOS and PPP increases ATP, inhibiting AMPK, which in turn releases PRPS1 from inhibitory phosphorylation and enhances purine nucleotide biosynthesis to drive melanoma proliferation.\",\n      \"method\": \"NDUFS3 knockdown/overexpression, AMPK activity assays, PRPS1 phosphorylation detection, metabolic flux analysis in melanoma cells\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — kinase-substrate relationship established by functional assays in cell lines, single lab\",\n      \"pmids\": [\"40404919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"EGF-activated CK2 phosphorylates the circadian protein CLOCK at S106, causing its nuclear export; cytosolic CLOCK then acetylates PRPS1 (and PRPS2) at K29, protecting them from HSC70-mediated degradation and enhancing GBM cell proliferation and migration.\",\n      \"method\": \"Site-directed mutagenesis, immunoprecipitation, immunofluorescence, subcellular fractionation, shRNA silencing, IHC in GBM specimens\",\n      \"journal\": \"Journal of neuro-oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing writer (CLOCK), modification site (K29ac), and functional consequence, single lab\",\n      \"pmids\": [\"40682742\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"The PRPS1 promoter contains a TATA-like sequence, CCAAT box, and three Sp1 binding sites, and a 2.0 kb 5'-flanking region drives reporter gene (CAT) expression with activity correlating with endogenous PRPS1 mRNA levels across cell lines, establishing these cis-elements as functional promoter elements.\",\n      \"method\": \"CAT/promoter fusion reporter assay in four cell lines, S1 nuclease and primer extension mapping of transcription start sites\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reporter assay identifying active promoter elements\",\n      \"pmids\": [\"1314091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NRF2 functions as an upstream transcription factor of PRPS1, driving its upregulation in melanoma; increased PRPS1 promotes melanoma cell proliferation, migration, invasion, and inhibits apoptosis both in vitro and in vivo.\",\n      \"method\": \"ChIP or transcription factor binding assay (NRF2-PRPS1), knockdown/overexpression in melanoma cell lines, xenograft tumor models\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — transcription factor–target relationship established, functional phenotype shown, single lab\",\n      \"pmids\": [\"36203561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SAM supplementation replenishes erythrocyte purine nucleotides (adenosine and guanosine) in an Arts syndrome (PRPS1 deficiency) patient; co-therapy with SAM and nicotinamide riboside further improved T-cell survival and function, supporting the role of PRPS1 in purine and NAD+ nucleotide supply in immune cells.\",\n      \"method\": \"Clinical supplementation trial with biochemical monitoring of erythrocyte nucleotide levels and T-cell functional assays\",\n      \"journal\": \"Molecular genetics and metabolism reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — functional rescue in a single patient with biochemical endpoint measurement\",\n      \"pmids\": [\"33532242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The mammalian PRPS enzyme complex comprises three isozymes (PRPS1, PRPS2, testis-restricted PRPS3) and two non-enzymatic associated proteins (PRPSAP1, PRPSAP2) that operate together as a large molecular weight complex with heterogeneous multimeric configurations; cells lacking PRPS2, PRPSAP1, and PRPSAP2 render PRPS1 into aberrant homo-oligomeric assemblies with diminished metabolic flux and impaired proliferative capacity.\",\n      \"method\": \"Isogenic fibroblast knockout clones in combinatorial assembly states, co-immunoprecipitation, metabolic flux analysis, proliferation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in isogenic cell panel, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.10.01.616059\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PRPS1 encodes phosphoribosyl pyrophosphate synthetase 1, a rate-limiting enzyme that phosphorylates ribose-5-phosphate to produce PRPP (the central precursor for de novo and salvage purine, pyrimidine, and pyridine nucleotide biosynthesis); its activity is allosterically inhibited by ADP/GDP and activated by inorganic phosphate, with filament assembly stabilizing the phosphate-binding site to provide an additional regulatory layer; disease mutations either abolish this feedback inhibition (superactivity/thiopurine resistance) or reduce catalytic activity (deafness, neuropathy, Arts syndrome); cell-cycle-dependent CDK1 phosphorylation at S103, AMPK-mediated inhibitory phosphorylation, and CLOCK-mediated K29 acetylation further tune PRPS1 activity to couple nucleotide supply to proliferative demand.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PRPS1 encodes phosphoribosyl pyrophosphate synthetase 1, the rate-limiting enzyme that converts ribose-5-phosphate to PRPP, the universal precursor for de novo and salvage synthesis of purine, pyrimidine, and NAD+ nucleotides, thereby coupling nucleotide supply to cell proliferation, DNA replication, and tissue maintenance. The enzyme is allosterically inhibited by ADP and GDP at two distinct sites, and gain-of-function mutations that disrupt this feedback cause enzyme superactivity with uric acid overproduction and thiopurine resistance in relapsed ALL, while loss-of-function mutations cause Arts syndrome, CMTX5 neuropathy, and X-linked nonsyndromic deafness (DFN2) [PMID:8253776, PMID:25962120, PMID:17701896, PMID:17701900, PMID:20021999]. PRPS1 assembles into filaments in both active and inhibited conformations; filament interfaces stabilize the phosphate-binding site to enhance catalytic activity, and disease-associated mutations alter filament assembly [PMID:36747094]. Activity is further tuned by CDK1 phosphorylation at S103 during S phase to fuel DNA replication, by AMPK-mediated inhibitory phosphorylation linking energy status to nucleotide output, and by CLOCK-mediated K29 acetylation that protects PRPS1 from HSC70-dependent degradation [PMID:31253668, PMID:40404919, PMID:40682742].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Defining the transcriptional architecture of PRPS1 established how its housekeeping expression is controlled, revealing a TATA-like element, CCAAT box, and Sp1 sites as functional cis-regulatory elements.\",\n      \"evidence\": \"CAT reporter assay with 2.0 kb 5'-flanking region across four cell lines, with S1 nuclease/primer extension mapping\",\n      \"pmids\": [\"1314091\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of cell-type-specific trans-acting factors beyond Sp1 not resolved\", \"Chromatin context not examined\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of N113S and D182H as feedback-resistance mutations established the molecular basis for allosteric inhibition of PRPS1 by purine nucleotides, answering how the enzyme is regulated at the product level.\",\n      \"evidence\": \"Recombinant mutant PRPS1 expressed in E. coli with in vitro enzymatic assay showing loss of ADP/GDP inhibition\",\n      \"pmids\": [\"8253776\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of allosteric sites not yet resolved at this time\", \"Whether additional residues participate in feedback not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that some PRPS1 superactivity results from accelerated transcription rather than coding mutations revealed a second disease mechanism and demonstrated that transcriptional output is rate-limiting for PRPP production.\",\n      \"evidence\": \"Northern blot, nuclear run-on, and Southern blot in patient fibroblasts/lymphoblasts\",\n      \"pmids\": [\"10066814\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factor(s) driving increased transcription not identified\", \"Epigenetic contribution not examined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Loss-of-function mutations were shown to cause two distinct X-linked diseases—Arts syndrome (L152P, Q133P) and CMTX5 neuropathy (E43D, M115T)—establishing that reduced PRPS1 activity impairs purine supply in neurons and immune cells.\",\n      \"evidence\": \"Enzymatic activity assays in patient erythrocytes and fibroblasts, segregation analysis in families\",\n      \"pmids\": [\"17701896\", \"17701900\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell-type-specific vulnerability (why neurons and hair cells are selectively affected) not explained\", \"No animal model validation at this stage\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Linking additional loss-of-function PRPS1 mutations to X-linked nonsyndromic deafness (DFN2) and demonstrating cochlear expression established that auditory hair cells are critically dependent on PRPS1-mediated nucleotide synthesis.\",\n      \"evidence\": \"Enzymatic assays in patient cells plus in situ hybridization of Prps1 in mouse cochlea\",\n      \"pmids\": [\"20021999\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether cochlear phenotype is purine-specific or involves pyrimidine/NAD+ depletion not resolved\", \"No conditional knockout in inner ear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Relapse-specific gain-of-function PRPS1 mutations were identified as a major mechanism of thiopurine resistance in childhood ALL, showing that loss of feedback inhibition constitutively activates de novo purine synthesis and competitively blocks thiopurine activation.\",\n      \"evidence\": \"Whole-exome sequencing of relapsed ALL, in vitro feedback inhibition assays, cell line drug resistance assays, and xenograft models\",\n      \"pmids\": [\"25962120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Frequency and clonal dynamics of PRPS1 mutations across ALL subtypes not fully mapped\", \"Structural mechanism of how mutations alter allosteric sites not yet visualized\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identification of miR-124 as a direct negative regulator of PRPS1 mRNA demonstrated a post-transcriptional control layer linking metabolic reprogramming to colorectal cancer proliferation.\",\n      \"evidence\": \"Luciferase reporter target validation, siRNA/overexpression rescue, xenograft tumor model\",\n      \"pmids\": [\"26248089\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Extent to which miR-124 regulation operates in non-malignant tissues not assessed\", \"Other miRNAs targeting PRPS1 not surveyed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Zebrafish PRPS1 knockdown phenocopied human deafness and Arts syndrome features—smaller otic vesicles, reduced hair cells, motor neuron defects, and immune cell loss—providing the first vertebrate genetic model and linking the phenotype to prolonged cell cycle from nucleotide insufficiency.\",\n      \"evidence\": \"CRISPR/morpholino knockdown in zebrafish with confocal imaging, hair cell counting, and cell cycle analysis\",\n      \"pmids\": [\"27425195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian conditional knockout not yet performed\", \"Contribution of pyrimidine vs. purine depletion not separated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The crystal structure of PRPS1 with the L191F superactivity mutation revealed how a single residue change disrupts both allosteric inhibitory sites, providing the first atomic-resolution explanation for feedback-resistant enzyme superactivity.\",\n      \"evidence\": \"X-ray crystal structure of human PRPS1 with mutant modeling and enzymatic confirmation\",\n      \"pmids\": [\"28742244\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Only one superactivity mutation structurally characterized\", \"Structure of full inhibited state not captured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"CDK1-mediated phosphorylation of PRPS1 at S103 during S phase established a direct cell-cycle-dependent mechanism for upregulating nucleotide production during DNA replication, linking PRPS1 to proliferative control in colorectal cancer.\",\n      \"evidence\": \"Cell-cycle synchronization, S103A mutagenesis, enzymatic activity assays, phospho-specific antibody staining in 184 colorectal cancer tissues\",\n      \"pmids\": [\"31253668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other CDK substrates in the PRPS complex are co-regulated not examined\", \"Phosphatase responsible for S103 dephosphorylation not identified\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"PRPS1 knockout in pluripotent stem cells caused DNA damage and apoptosis, demonstrating that PRPS1-dependent purine biosynthesis is essential for stem cell genome integrity and survival.\",\n      \"evidence\": \"PRPS1 knockout in PSCs with UHPLC-MS metabolite profiling, apoptosis, and DNA damage assays\",\n      \"pmids\": [\"33493137\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PRPS2 can compensate in other stem cell contexts not tested\", \"Downstream nucleotide species responsible for DNA damage not pinpointed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"NRF2 was identified as an upstream transcriptional activator of PRPS1 in melanoma, providing a mechanism by which oxidative stress signaling rewires nucleotide metabolism to support tumor growth.\",\n      \"evidence\": \"ChIP/transcription factor binding assay, knockdown/overexpression in melanoma lines, xenograft models\",\n      \"pmids\": [\"36203561\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct NRF2 binding site in PRPS1 promoter not mapped at nucleotide resolution\", \"Not confirmed in non-melanoma contexts\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"PRPS2 mutations in relapsed ALL were shown to destabilize the PRPS1/2 hexamer interface and reduce nucleotide feedback inhibition, demonstrating that the hetero-oligomeric context of PRPS1 is critical for proper allosteric regulation.\",\n      \"evidence\": \"Ultra-deep sequencing, in vitro enzyme assays, ADP/GDP feedback inhibition assays, UPLC-MS/MS metabolomics, xenograft models\",\n      \"pmids\": [\"36742181\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of PRPS1:PRPS2 in normal vs. leukemic cells not determined\", \"Whether PRPSAP1/AP2 modulate this phenotype not addressed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Cryo-EM structures of PRPS1 filaments in active and inhibited states revealed that polymerization stabilizes the phosphate-binding site and couples catalysis with product release across adjacent active sites, establishing filament assembly as a fundamental regulatory mechanism.\",\n      \"evidence\": \"Cryo-EM structure determination of filaments in multiple states with disease-variant mutagenesis\",\n      \"pmids\": [\"36747094\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo evidence for filament formation not yet obtained\", \"How filament assembly/disassembly is regulated by cellular signals is unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"AMPK-mediated inhibitory phosphorylation of PRPS1 established a direct energy-sensing mechanism that suppresses nucleotide biosynthesis under metabolic stress, linking OXPHOS status to PRPS1 output in melanoma.\",\n      \"evidence\": \"NDUFS3 knockdown/overexpression, AMPK activity assays, PRPS1 phosphorylation detection, metabolic flux analysis in melanoma cells\",\n      \"pmids\": [\"40404919\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific AMPK phosphorylation site(s) on PRPS1 not mapped\", \"Not confirmed in non-melanoma cell types\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CLOCK-mediated K29 acetylation of PRPS1 was shown to protect it from HSC70-dependent degradation, revealing a circadian/signaling-dependent post-translational stabilization mechanism relevant to glioblastoma proliferation.\",\n      \"evidence\": \"Site-directed mutagenesis, immunoprecipitation, immunofluorescence, subcellular fractionation, shRNA silencing in GBM cells\",\n      \"pmids\": [\"40682742\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Deacetylase(s) that reverse K29 acetylation not identified\", \"Circadian oscillation of PRPS1 protein levels not directly demonstrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"PRPS1 deficiency was linked to NAD+/SIRT3/SOD2 pathway downregulation and mitochondrial dysfunction in auditory cells, providing a mechanistic explanation for hair cell vulnerability in PRPS1-associated deafness and suggesting NAD+ precursor supplementation as a rescue strategy.\",\n      \"evidence\": \"siRNA knockdown in HEI-OC1 cells with ROS/mitochondrial assays and NMN rescue; zebrafish mutant PRPS1 overexpression model\",\n      \"pmids\": [\"40677922\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NAD+ depletion or purine depletion is the primary cause of hair cell death not fully dissected\", \"NMN rescue only partial; in vivo mammalian validation lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: how PRPS1 filament assembly and disassembly are regulated in vivo; what determines cell-type-specific vulnerability to PRPS1 deficiency (neurons, hair cells, immune cells); and the precise stoichiometry and regulatory roles of PRPSAP1/PRPSAP2 within the native PRPS complex.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo evidence for filament dynamics\", \"Conditional tissue-specific knockout in mammals not performed\", \"Native complex stoichiometry and its regulation remain poorly defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 6, 7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 2, 6, 7, 9, 12]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [7, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\n      \"PRPS hexamer (PRPS1/PRPS2/PRPSAP1/PRPSAP2)\",\n      \"PRPS1 filament\"\n    ],\n    \"partners\": [\n      \"PRPS2\",\n      \"PRPSAP1\",\n      \"PRPSAP2\",\n      \"CDK1\",\n      \"AMPK\",\n      \"CLOCK\",\n      \"HSC70\",\n      \"NRF2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}