{"gene":"TPPP2","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2006,"finding":"TPPP2 (p18/p25beta) was found to be a more structurally ordered protein compared to TPPP1/p25 and TPPP3/p20, and unlike TPPP1 and p20, TPPP2 (p18) does not cross-link microtubules and distributes homogeneously within the cytosol of transfected HeLa cells rather than associating with microtubule bundles.","method":"Recombinant protein characterization, in vitro microtubule bundling assays, transfection of HeLa cells with fluorescent constructs, electron microscopy","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro assay plus cellular localization in transfected cells, single lab, multiple orthogonal methods","pmids":["17105200"],"is_preprint":false},{"year":2017,"finding":"TPPP2 does not bind tubulin and does not promote tubulin polymerization or microtubule bundling, in contrast to TPPP1 and TPPP3 which retain these activities; this establishes that TPPP2 has markedly reduced/absent microtubule-binding and bundling capacity within the TPPP family.","method":"Biochemical tubulin binding and polymerization assays, bioinformatics, spectroscopic analysis, electron microscopy","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assays, single lab, multiple orthogonal methods confirming negative result for TPPP2","pmids":["28106390"],"is_preprint":false},{"year":2019,"finding":"TPPP2 protein localizes to elongating spermatids (stages IV-VIII of the seminiferous epithelial cycle) and in mature sperm in the epididymis; knockout of Tppp2 in mice causes male subfertility with decreased sperm count and motility, increased mitochondrial structural abnormalities (irregular mitochondria lacking lamellar cristae), abnormal expression of electron transfer chain molecules, lower ATP levels, decreased mitochondrial membrane potential, and increased apoptotic index in sperm.","method":"Immunolocalization, Tppp2 knockout mouse model, sperm motility assays, ATP measurement, mitochondrial membrane potential assay, electron microscopy, apoptosis assays","journal":"Journal of cellular and molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with specific cellular phenotype readouts plus multiple orthogonal biochemical measurements, single lab but highly systematic","pmids":["30680919"],"is_preprint":false},{"year":2019,"finding":"TPPP2 interacts with eukaryotic translation elongation factor 1 beta (eEF1B), suggesting TPPP2 may affect translation of specific proteins relevant to sperm mitochondrial function.","method":"Co-immunoprecipitation / protein interaction assay (identified as potential interactive protein)","journal":"Journal of cellular and molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP/pulldown experiment, single lab, described as 'potential' interaction without full validation","pmids":["30680919"],"is_preprint":false},{"year":2021,"finding":"TPPP2 forms part of a cytoplasmic protein network with CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 during spermiogenesis, as shown by endogenous co-immunoprecipitation and immunostaining in mouse testes.","method":"Endogenous immunoprecipitation, immunostaining, proteomic analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — endogenous Co-IP plus immunostaining, single lab, two orthogonal methods","pmids":["34231842"],"is_preprint":false},{"year":1997,"finding":"The protein encoded by the p25beta locus (an alias for TPPP2) contains a conserved chromodomain in the N-terminal region and a heterochromatin binding domain in the C-terminal region; antibodies specific to the C-terminal domain (amino acids 70-185) show nucleoplasmic, heterochromatin, and centromeric staining in immunofluorescence, while N-terminal-specific antibodies show no staining; the protein associates with centromeres most prominently at anaphase.","method":"cDNA cloning, affinity-purified antibodies with domain-specific immunofluorescence, metaphase chromosome spreads","journal":"Chromosoma","confidence":"Low","confidence_rationale":"Tier 3 / Weak — NOTE: this paper describes HP1Hsbeta (p25beta), which in later literature is clarified to be CBX1/HP1beta, not TPPP2; the alias 'p25beta' was used for both proteins. The corpus identifies p25beta as an alias of TPPP2 per HGNC, but this paper's described function (chromodomain, heterochromatin) is inconsistent with TPPP2's established microtubule/sperm biology, suggesting likely alias collision. Confidence assigned as Low.","pmids":["9169582"],"is_preprint":false}],"current_model":"TPPP2 is a member of the tubulin polymerization promoting protein family that, unlike its paralogs TPPP1 and TPPP3, lacks microtubule-binding and bundling activity and distributes diffusely in the cytosol; it localizes to elongating spermatids and mature sperm, where it is required for normal mitochondrial structure and function, sperm motility, and male fertility, likely through effects on mitochondrial ATP production and interactions with translation elongation factor eEF1B and a cytoplasmic complex including CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 during spermiogenesis."},"narrative":{"mechanistic_narrative":"TPPP2 (p18/p25beta) is a member of the tubulin polymerization promoting protein family that functions in spermiogenesis and male fertility rather than in microtubule organization [PMID:30680919]. Despite its family membership, TPPP2 does not bind tubulin and does not promote tubulin polymerization or microtubule bundling — activities retained by its paralogs TPPP1 and TPPP3 — and instead distributes homogeneously in the cytosol of transfected cells [PMID:17105200, PMID:28106390]. TPPP2 protein localizes to elongating spermatids and mature sperm, and its loss in knockout mice causes male subfertility with reduced sperm count and motility together with mitochondrial structural defects, abnormal electron transfer chain expression, lowered ATP levels, decreased mitochondrial membrane potential, and increased sperm apoptosis [PMID:30680919]. During spermiogenesis TPPP2 participates in a cytoplasmic protein network with CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 [PMID:34231842]. Beyond these findings, the molecular mechanism by which TPPP2 supports sperm mitochondrial function has not been resolved in the available corpus.","teleology":[{"year":2006,"claim":"Established that TPPP2, despite belonging to the TPPP family, does not behave like its microtubule-bundling paralogs, raising the question of what distinct function it serves.","evidence":"Recombinant protein characterization, in vitro microtubule bundling assays, and localization of fluorescent constructs in transfected HeLa cells","pmids":["17105200"],"confidence":"Medium","gaps":["Cytosolic diffuse distribution leaves the native cellular role undefined","Tested only in a heterologous HeLa context"]},{"year":2017,"claim":"Resolved whether TPPP2 retains any tubulin activity, confirming it lacks tubulin binding, polymerization, and bundling capacity and diverges functionally from TPPP1/TPPP3.","evidence":"In vitro tubulin binding and polymerization assays, spectroscopy, and electron microscopy","pmids":["28106390"],"confidence":"Medium","gaps":["A negative result that does not identify the actual molecular activity of TPPP2","No alternative binding partners or substrates identified in this work"]},{"year":2019,"claim":"Defined the physiological role of TPPP2 by showing it is expressed in spermatids and sperm and is required for normal sperm number, motility, and mitochondrial integrity, linking TPPP2 to male fertility.","evidence":"Tppp2 knockout mouse with immunolocalization, sperm motility assays, ATP and mitochondrial membrane potential measurements, electron microscopy, and apoptosis assays","pmids":["30680919"],"confidence":"High","gaps":["Whether mitochondrial defects are a direct or downstream consequence of TPPP2 loss is unresolved","The molecular activity connecting TPPP2 to ATP production is not established"]},{"year":2019,"claim":"Offered a candidate mechanism by identifying eEF1B as a TPPP2 interactor, hinting at a role in localized translation relevant to mitochondrial function.","evidence":"Co-immunoprecipitation identifying eEF1B as a potential interactor","pmids":["30680919"],"confidence":"Low","gaps":["Single Co-IP described as a potential interaction without reciprocal validation","No demonstration that TPPP2 influences translation of specific mitochondrial proteins"]},{"year":2021,"claim":"Placed TPPP2 within a defined cytoplasmic protein network during spermiogenesis, indicating it operates in a multiprotein assembly rather than alone.","evidence":"Endogenous co-immunoprecipitation, immunostaining, and proteomic analysis in mouse testes","pmids":["34231842"],"confidence":"Medium","gaps":["Direct versus indirect nature of each interaction within the network is undefined","Functional consequence of the network for sperm formation is not dissected"]},{"year":null,"claim":"The molecular activity of TPPP2 and the mechanism by which it maintains sperm mitochondrial structure and ATP production remain unknown.","evidence":"","pmids":[],"confidence":"Low","gaps":["No biochemical activity assigned after exclusion of tubulin binding","No validated mechanistic link between TPPP2 interactors and the mitochondrial phenotype"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[2,4]}],"complexes":[],"partners":["EEF1B","CFAP65","MNS1","RSPH1","ZPBP1","SPACA1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P59282","full_name":"Tubulin polymerization-promoting protein family member 2","aliases":["Protein p25-beta","TPPP/p18"],"length_aa":170,"mass_kda":18.5,"function":"Probable regulator of microtubule dynamics required for sperm motility (Probable). In contrast to other members of the family, has no microtubule bundling activity (PubMed:17105200)","subcellular_location":"Cytoplasm, cytosol; Cell projection, cilium, flagellum","url":"https://www.uniprot.org/uniprotkb/P59282/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TPPP2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TPPP2","total_profiled":1310},"omim":[{"mim_id":"616957","title":"TUBULIN POLYMERIZATION-PROMOTING PROTEIN FAMILY, MEMBER 3; TPPP3","url":"https://www.omim.org/entry/616957"},{"mim_id":"616956","title":"TUBULIN POLYMERIZATION-PROMOTING PROTEIN FAMILY, MEMBER 2; TPPP2","url":"https://www.omim.org/entry/616956"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Connecting piece","reliability":"Approved"},{"location":"Mid piece","reliability":"Approved"},{"location":"Principal piece","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"testis","ntpm":251.0}],"url":"https://www.proteinatlas.org/search/TPPP2"},"hgnc":{"alias_symbol":["p25beta","p18","CT152"],"prev_symbol":["C14orf8"]},"alphafold":{"accession":"P59282","domains":[{"cath_id":"1.10.238.10","chopping":"1-107","consensus_level":"medium","plddt":87.1237,"start":1,"end":107},{"cath_id":"-","chopping":"109-149","consensus_level":"medium","plddt":83.701,"start":109,"end":149}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P59282","model_url":"https://alphafold.ebi.ac.uk/files/AF-P59282-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P59282-F1-predicted_aligned_error_v6.png","plddt_mean":85.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TPPP2","jax_strain_url":"https://www.jax.org/strain/search?query=TPPP2"},"sequence":{"accession":"P59282","fasta_url":"https://rest.uniprot.org/uniprotkb/P59282.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P59282/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P59282"}},"corpus_meta":[{"pmid":"17105200","id":"PMC_17105200","title":"Tubulin polymerization promoting proteins (TPPPs): members of a new family with distinct structures and functions.","date":"2006","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17105200","citation_count":83,"is_preprint":false},{"pmid":"9169582","id":"PMC_9169582","title":"Heterochromatin protein HP1Hsbeta (p25beta) and its localization with centromeres in mitosis.","date":"1997","source":"Chromosoma","url":"https://pubmed.ncbi.nlm.nih.gov/9169582","citation_count":61,"is_preprint":false},{"pmid":"23436708","id":"PMC_23436708","title":"Scanning of novel cancer/testis proteins by human testis proteomic analysis.","date":"2013","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/23436708","citation_count":55,"is_preprint":false},{"pmid":"30680919","id":"PMC_30680919","title":"Deficiency of TPPP2, a factor linked to oligoasthenozoospermia, causes subfertility in male mice.","date":"2019","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30680919","citation_count":44,"is_preprint":false},{"pmid":"33292187","id":"PMC_33292187","title":"A systems biology framework integrating GWAS and RNA-seq to shed light on the molecular basis of sperm quality in swine.","date":"2020","source":"Genetics, selection, evolution : GSE","url":"https://pubmed.ncbi.nlm.nih.gov/33292187","citation_count":44,"is_preprint":false},{"pmid":"34231842","id":"PMC_34231842","title":"CFAP65 is required in the acrosome biogenesis and mitochondrial sheath assembly during spermiogenesis.","date":"2021","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34231842","citation_count":36,"is_preprint":false},{"pmid":"10759029","id":"PMC_10759029","title":"Identification of an alpha-helical epitope region on the PM/Scl-100 autoantigen with structural homology to a region on the heterochromatin p25beta autoantigen using immobilized overlapping synthetic peptides.","date":"2000","source":"Journal of molecular medicine (Berlin, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/10759029","citation_count":32,"is_preprint":false},{"pmid":"30820981","id":"PMC_30820981","title":"Comparative proteomic analysis of high- and low-fertile buffalo bull spermatozoa for identification of fertility-associated proteins.","date":"2019","source":"Reproduction in domestic animals = Zuchthygiene","url":"https://pubmed.ncbi.nlm.nih.gov/30820981","citation_count":30,"is_preprint":false},{"pmid":"22711244","id":"PMC_22711244","title":"Genetic architecture of resilience of executive functioning.","date":"2012","source":"Brain imaging and behavior","url":"https://pubmed.ncbi.nlm.nih.gov/22711244","citation_count":23,"is_preprint":false},{"pmid":"37782577","id":"PMC_37782577","title":"Bull Sperm SWATH-MS-Based Proteomics Reveals Link between High Fertility and Energy Production, Motility Structures, and Sperm-Oocyte Interaction.","date":"2023","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/37782577","citation_count":21,"is_preprint":false},{"pmid":"28106390","id":"PMC_28106390","title":"Tubulin Binding and Polymerization Promoting Properties of Tubulin Polymerization Promoting Proteins Are Evolutionarily Conserved.","date":"2017","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28106390","citation_count":21,"is_preprint":false},{"pmid":"9462868","id":"PMC_9462868","title":"Immunological characterization of heterochromatin protein p25beta autoantibodies and relationship with centromere autoantibodies and pulmonary fibrosis in systemic scleroderma.","date":"1998","source":"Journal of molecular medicine (Berlin, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/9462868","citation_count":18,"is_preprint":false},{"pmid":"36277216","id":"PMC_36277216","title":"Quantitative phosphoproteomics analyses reveal the regulatory mechanisms related to frozen-thawed sperm capacitation and acrosome reaction in yak (Bos grunniens).","date":"2022","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/36277216","citation_count":15,"is_preprint":false},{"pmid":"29948331","id":"PMC_29948331","title":"Whole-exome sequencing in maya indigenous families: variant in PPP1R3A is associated with type 2 diabetes.","date":"2018","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/29948331","citation_count":13,"is_preprint":false},{"pmid":"25576359","id":"PMC_25576359","title":"On the tubulin polymerization promoting proteins of zebrafish.","date":"2015","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/25576359","citation_count":8,"is_preprint":false},{"pmid":"23053195","id":"PMC_23053195","title":"A fish-specific member of the TPPP protein family?","date":"2012","source":"Journal of molecular evolution","url":"https://pubmed.ncbi.nlm.nih.gov/23053195","citation_count":6,"is_preprint":false},{"pmid":"40041504","id":"PMC_40041504","title":"Identification of reproductive performance in Bali-polled bulls using computer-assisted semen analysis and plasma seminal proteomics.","date":"2025","source":"Veterinary world","url":"https://pubmed.ncbi.nlm.nih.gov/40041504","citation_count":4,"is_preprint":false},{"pmid":"40766128","id":"PMC_40766128","title":"Large-scale plasma proteomics uncovers preclinical molecular signatures of Parkinson's disease and overlap with other neurodegenerative disorders.","date":"2025","source":"medRxiv : the preprint server for health sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40766128","citation_count":1,"is_preprint":false},{"pmid":"41148789","id":"PMC_41148789","title":"Diverse Roles of Tubulin Polymerization Promoting Protein 3 (TPPP3) in Human Health and Disease.","date":"2025","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/41148789","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.30.25332433","title":"Large-scale plasma proteomics uncovers preclinical molecular signatures of Parkinson’s disease and overlap with other neurodegenerative disorders","date":"2025-07-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.30.25332433","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12544,"output_tokens":1665,"usd":0.031303,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8420,"output_tokens":1876,"usd":0.0445,"stage2_stop_reason":"end_turn"},"total_usd":0.075803,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"TPPP2 (p18/p25beta) was found to be a more structurally ordered protein compared to TPPP1/p25 and TPPP3/p20, and unlike TPPP1 and p20, TPPP2 (p18) does not cross-link microtubules and distributes homogeneously within the cytosol of transfected HeLa cells rather than associating with microtubule bundles.\",\n      \"method\": \"Recombinant protein characterization, in vitro microtubule bundling assays, transfection of HeLa cells with fluorescent constructs, electron microscopy\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro assay plus cellular localization in transfected cells, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"17105200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TPPP2 does not bind tubulin and does not promote tubulin polymerization or microtubule bundling, in contrast to TPPP1 and TPPP3 which retain these activities; this establishes that TPPP2 has markedly reduced/absent microtubule-binding and bundling capacity within the TPPP family.\",\n      \"method\": \"Biochemical tubulin binding and polymerization assays, bioinformatics, spectroscopic analysis, electron microscopy\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assays, single lab, multiple orthogonal methods confirming negative result for TPPP2\",\n      \"pmids\": [\"28106390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TPPP2 protein localizes to elongating spermatids (stages IV-VIII of the seminiferous epithelial cycle) and in mature sperm in the epididymis; knockout of Tppp2 in mice causes male subfertility with decreased sperm count and motility, increased mitochondrial structural abnormalities (irregular mitochondria lacking lamellar cristae), abnormal expression of electron transfer chain molecules, lower ATP levels, decreased mitochondrial membrane potential, and increased apoptotic index in sperm.\",\n      \"method\": \"Immunolocalization, Tppp2 knockout mouse model, sperm motility assays, ATP measurement, mitochondrial membrane potential assay, electron microscopy, apoptosis assays\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with specific cellular phenotype readouts plus multiple orthogonal biochemical measurements, single lab but highly systematic\",\n      \"pmids\": [\"30680919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TPPP2 interacts with eukaryotic translation elongation factor 1 beta (eEF1B), suggesting TPPP2 may affect translation of specific proteins relevant to sperm mitochondrial function.\",\n      \"method\": \"Co-immunoprecipitation / protein interaction assay (identified as potential interactive protein)\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP/pulldown experiment, single lab, described as 'potential' interaction without full validation\",\n      \"pmids\": [\"30680919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TPPP2 forms part of a cytoplasmic protein network with CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 during spermiogenesis, as shown by endogenous co-immunoprecipitation and immunostaining in mouse testes.\",\n      \"method\": \"Endogenous immunoprecipitation, immunostaining, proteomic analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — endogenous Co-IP plus immunostaining, single lab, two orthogonal methods\",\n      \"pmids\": [\"34231842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The protein encoded by the p25beta locus (an alias for TPPP2) contains a conserved chromodomain in the N-terminal region and a heterochromatin binding domain in the C-terminal region; antibodies specific to the C-terminal domain (amino acids 70-185) show nucleoplasmic, heterochromatin, and centromeric staining in immunofluorescence, while N-terminal-specific antibodies show no staining; the protein associates with centromeres most prominently at anaphase.\",\n      \"method\": \"cDNA cloning, affinity-purified antibodies with domain-specific immunofluorescence, metaphase chromosome spreads\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — NOTE: this paper describes HP1Hsbeta (p25beta), which in later literature is clarified to be CBX1/HP1beta, not TPPP2; the alias 'p25beta' was used for both proteins. The corpus identifies p25beta as an alias of TPPP2 per HGNC, but this paper's described function (chromodomain, heterochromatin) is inconsistent with TPPP2's established microtubule/sperm biology, suggesting likely alias collision. Confidence assigned as Low.\",\n      \"pmids\": [\"9169582\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TPPP2 is a member of the tubulin polymerization promoting protein family that, unlike its paralogs TPPP1 and TPPP3, lacks microtubule-binding and bundling activity and distributes diffusely in the cytosol; it localizes to elongating spermatids and mature sperm, where it is required for normal mitochondrial structure and function, sperm motility, and male fertility, likely through effects on mitochondrial ATP production and interactions with translation elongation factor eEF1B and a cytoplasmic complex including CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 during spermiogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TPPP2 (p18/p25beta) is a member of the tubulin polymerization promoting protein family that functions in spermiogenesis and male fertility rather than in microtubule organization [#2]. Despite its family membership, TPPP2 does not bind tubulin and does not promote tubulin polymerization or microtubule bundling — activities retained by its paralogs TPPP1 and TPPP3 — and instead distributes homogeneously in the cytosol of transfected cells [#0, #1]. TPPP2 protein localizes to elongating spermatids and mature sperm, and its loss in knockout mice causes male subfertility with reduced sperm count and motility together with mitochondrial structural defects, abnormal electron transfer chain expression, lowered ATP levels, decreased mitochondrial membrane potential, and increased sperm apoptosis [#2]. During spermiogenesis TPPP2 participates in a cytoplasmic protein network with CFAP65, MNS1, RSPH1, ZPBP1, and SPACA1 [#4]. Beyond these findings, the molecular mechanism by which TPPP2 supports sperm mitochondrial function has not been resolved in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that TPPP2, despite belonging to the TPPP family, does not behave like its microtubule-bundling paralogs, raising the question of what distinct function it serves.\",\n      \"evidence\": \"Recombinant protein characterization, in vitro microtubule bundling assays, and localization of fluorescent constructs in transfected HeLa cells\",\n      \"pmids\": [\"17105200\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cytosolic diffuse distribution leaves the native cellular role undefined\", \"Tested only in a heterologous HeLa context\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved whether TPPP2 retains any tubulin activity, confirming it lacks tubulin binding, polymerization, and bundling capacity and diverges functionally from TPPP1/TPPP3.\",\n      \"evidence\": \"In vitro tubulin binding and polymerization assays, spectroscopy, and electron microscopy\",\n      \"pmids\": [\"28106390\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"A negative result that does not identify the actual molecular activity of TPPP2\", \"No alternative binding partners or substrates identified in this work\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the physiological role of TPPP2 by showing it is expressed in spermatids and sperm and is required for normal sperm number, motility, and mitochondrial integrity, linking TPPP2 to male fertility.\",\n      \"evidence\": \"Tppp2 knockout mouse with immunolocalization, sperm motility assays, ATP and mitochondrial membrane potential measurements, electron microscopy, and apoptosis assays\",\n      \"pmids\": [\"30680919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mitochondrial defects are a direct or downstream consequence of TPPP2 loss is unresolved\", \"The molecular activity connecting TPPP2 to ATP production is not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Offered a candidate mechanism by identifying eEF1B as a TPPP2 interactor, hinting at a role in localized translation relevant to mitochondrial function.\",\n      \"evidence\": \"Co-immunoprecipitation identifying eEF1B as a potential interactor\",\n      \"pmids\": [\"30680919\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP described as a potential interaction without reciprocal validation\", \"No demonstration that TPPP2 influences translation of specific mitochondrial proteins\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed TPPP2 within a defined cytoplasmic protein network during spermiogenesis, indicating it operates in a multiprotein assembly rather than alone.\",\n      \"evidence\": \"Endogenous co-immunoprecipitation, immunostaining, and proteomic analysis in mouse testes\",\n      \"pmids\": [\"34231842\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect nature of each interaction within the network is undefined\", \"Functional consequence of the network for sperm formation is not dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular activity of TPPP2 and the mechanism by which it maintains sperm mitochondrial structure and ATP production remain unknown.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No biochemical activity assigned after exclusion of tubulin binding\", \"No validated mechanistic link between TPPP2 interactors and the mitochondrial phenotype\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"eEF1B\", \"CFAP65\", \"MNS1\", \"RSPH1\", \"ZPBP1\", \"SPACA1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}