{"gene":"PRSS55","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2018,"finding":"PRSS55 is a GPI-anchored membrane protein specifically expressed in adult mouse testis, localized to the luminal side of seminiferous tubules and sperm acrosome. Knockout of Prss55 results in impaired in vivo sperm migration from uterus to oviduct and defective sperm-egg recognition/binding to zona-intact and zona-free oocytes. Mature ADAM3 is almost undetectable in Prss55-/- sperm (precursor ADAM3 is unchanged in testis), though ADAM3 does not directly interact with PRSS55 by co-immunoprecipitation.","method":"Knockout mice (Prss55-/-), in vivo/in vitro fertilization assays, immunoprecipitation, immunofluorescence, microarray analysis","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple defined phenotypic readouts, GPI-anchor localization, ADAM3 maturation assay; replicated by independent labs","pmids":["30032357"],"is_preprint":false},{"year":2020,"finding":"PRSS55, but not its paralog PRSS51, is required for male fertility in mice. Prss55 KO mice phenocopy double-KO mice, showing impaired sperm migration through the uterotubal junction (UTJ) and impaired sperm-zona pellucida (ZP) binding. ADAM3 protein is lost from Prss55-/- epididymal spermatozoa, indicating PRSS55 stabilizes ADAM3 during epididymal maturation for efficient UTJ migration and ZP binding.","method":"CRISPR/Cas9 single and double knockout mice, fertility trials, sperm migration assays, zona pellucida binding assays, western blot for ADAM3","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via single vs. double KO, multiple orthogonal functional assays, independent replication of ADAM3 loss","pmids":["32301961"],"is_preprint":false},{"year":2021,"finding":"Deletion of all Prss55 transcripts leads to sperm structural abnormalities including deficient '9+2' microtubule arrangement, damaged peripheral dense fibers, and defective mitochondrial cristae. Prss55-/- sperm show decreased expression of electron transport chain molecules and lower ATP content. PRSS55 may function by activating type II muscle myosin in the testis, involved in cytoskeleton translocation.","method":"Knockout mice targeting all transcripts, transmission electron microscopy, ATP measurement, proteomics/western blot for ETC molecules","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — KO with structural and metabolic phenotypic readouts, but myosin activation is preliminary/speculative","pmids":["33417308"],"is_preprint":false},{"year":2008,"finding":"Human PRSS55 (described as T-SP1) is a membrane-anchored chymotrypsin (S1)-like serine protease encoded on chromosome 8p with a catalytic triad of His108, Asp156, and Ser250. Alternative splicing generates three variants; only the T-SP1/1 variant contains a C-terminal hydrophobic domain enabling GPI/membrane anchoring. The protein is expressed in Leydig and Sertoli cells of testis and in epithelial cells of ductuli efferentes.","method":"RACE, sequencing, domain analysis, polyclonal antibody immunohistochemistry","journal":"Biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical characterization of domain architecture and catalytic triad, localization by IHC with specific antibody","pmids":["18844450"],"is_preprint":false},{"year":2025,"finding":"Human PRSS55 expressed transgenically in Prss55 null mice can functionally rescue male fertility, with the intracellularly-tagged version (RES TM) restoring fertility to levels comparable to wild-type controls, validating functional conservation of human PRSS55. The extracellularly-tagged version (RES GPI) only partially restored fertility, indicating the C-terminal tag position (and thus membrane orientation) affects function.","method":"Transgenic rescue in Prss55-/- mice, continuous mating fertility trials, sperm parameter analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — transgenic rescue with functional readout; single lab study","pmids":["40764777"],"is_preprint":false},{"year":2025,"finding":"PRSS55 is localized to mitochondria in sperm (validated by immunofluorescence in sperm and transfected NIH-3T3 cells, and immunoblotting of testis and HEK293 cells). Prss55-/- testes and sperm show impaired mitochondrial function including low ATP production and decreased mitochondrial membrane potential. Overexpression of PRSS55 in HEK293 cells increases ATP production and NAD+/NADH ratio. By proteomics and metabolomics, PRSS55 loss leads to accumulation of branched-chain amino acids (BCAAs: valine, leucine, isoleucine) in testes. Co-IP and LC-MS/MS validated that PRSS55 physically interacts with BCKDK (branched-chain alpha-ketoacid dehydrogenase kinase) and BCKDHA (branched-chain ketoacid dehydrogenase E1α), two key enzymes of BCAA catabolism.","method":"Immunofluorescence, immunoblotting, subcellular fractionation, overexpression in HEK293 cells (ATP/NAD+ assays), proteomics, metabolomics, Co-IP, LC-MS/MS","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, LC-MS/MS, metabolomics, in vitro overexpression assay), single lab study","pmids":["41444608"],"is_preprint":false},{"year":2022,"finding":"A homozygous missense mutation in human PRSS55 (c.575C>T, p.A192V) causes male infertility with teratozoospermia. The mutation alters PRSS55 protein conformation and causes a sharp decrease in PRSS55 protein levels in patient spermatozoa, as demonstrated by immunofluorescence and western blot. PRSS55 localizes to the head and flagella of human spermatids and epididymal spermatozoa.","method":"Whole exome sequencing, Sanger sequencing, western blot, immunofluorescence, electron microscopy","journal":"Reproductive biomedicine online","confidence":"Medium","confidence_rationale":"Tier 3 — human patient variant with protein-level validation; single case","pmids":["35821214"],"is_preprint":false}],"current_model":"PRSS55 is a testis-specific, GPI-anchored chymotrypsin-like serine protease that localizes to the sperm acrosome and mitochondria, where it stabilizes ADAM3 protein during epididymal maturation to enable sperm migration through the uterotubal junction and zona pellucida binding, and additionally interacts with BCKDK and BCKDHA to regulate branched-chain amino acid metabolism and mitochondrial energy production in sperm."},"narrative":{"teleology":[{"year":2008,"claim":"Initial molecular characterization established that PRSS55 is a membrane-anchored S1-family serine protease with a complete catalytic triad and GPI-anchoring capability, resolving its domain architecture and testicular cell-type expression.","evidence":"RACE cloning, domain analysis, and immunohistochemistry on human testis","pmids":["18844450"],"confidence":"Medium","gaps":["No enzymatic activity or substrate demonstrated","Functional role in reproduction not yet tested","GPI-anchoring not confirmed biochemically (inferred from hydrophobic domain)"]},{"year":2018,"claim":"Knockout studies revealed that PRSS55 is required for sperm migration from uterus to oviduct and for sperm-zona pellucida binding, and that it controls ADAM3 maturation on epididymal sperm without direct physical interaction with ADAM3.","evidence":"Prss55-/- knockout mice with in vivo/in vitro fertilization assays, co-immunoprecipitation, immunofluorescence","pmids":["30032357"],"confidence":"High","gaps":["Mechanism by which PRSS55 stabilizes ADAM3 indirectly remains unknown","No proteolytic substrate identified","Whether catalytic activity is required for function not tested"]},{"year":2020,"claim":"Genetic epistasis analysis demonstrated that PRSS55, but not its paralog PRSS51, is the functionally relevant protease for UTJ migration and ZP binding, independently confirming ADAM3 loss as a key downstream consequence.","evidence":"CRISPR/Cas9 single and double knockout mice with fertility trials and sperm migration assays","pmids":["32301961"],"confidence":"High","gaps":["Whether PRSS55 acts enzymatically or as a scaffold/chaperone is unresolved","Downstream signaling between PRSS55 loss and ADAM3 destabilization not mapped"]},{"year":2021,"claim":"Complete deletion of Prss55 transcripts revealed sperm ultrastructural defects (disrupted 9+2 axoneme, damaged dense fibers, defective mitochondrial cristae) and decreased ATP, expanding the functional role beyond ADAM3 to mitochondrial and cytoskeletal integrity.","evidence":"Knockout mice with transmission electron microscopy, ATP measurement, and proteomics","pmids":["33417308"],"confidence":"Medium","gaps":["Proposed myosin activation mechanism is preliminary and not validated by direct interaction or activity assays","Relationship between mitochondrial defects and ADAM3 loss not clarified","Whether structural defects are primary or secondary to metabolic dysfunction is unclear"]},{"year":2022,"claim":"Identification of a human PRSS55 missense variant (p.A192V) causing teratozoospermia established PRSS55 as a human male infertility gene and demonstrated that protein stability is critical for function.","evidence":"Whole exome sequencing of infertile patient, protein-level validation by western blot and immunofluorescence","pmids":["35821214"],"confidence":"Medium","gaps":["Single family reported; replication in independent cohorts needed","Whether p.A192V disrupts catalytic activity versus protein folding not distinguished","No functional rescue experiment performed"]},{"year":2025,"claim":"Transgenic rescue with human PRSS55 confirmed functional conservation across species and showed that C-terminal membrane orientation (intracellular vs. extracellular tag) critically affects fertility restoration.","evidence":"Transgenic rescue in Prss55-/- mice with continuous mating fertility trials","pmids":["40764777"],"confidence":"Medium","gaps":["Whether partial rescue by GPI-tagged version reflects impaired trafficking, folding, or activity is unknown","Single lab study without independent replication"]},{"year":2025,"claim":"Mitochondrial localization and physical interaction with BCKDK and BCKDHA linked PRSS55 to branched-chain amino acid catabolism and mitochondrial energy production, providing a mechanistic basis for the ATP deficiency observed in knockout sperm.","evidence":"Co-IP, LC-MS/MS, metabolomics, ATP and NAD+ assays in knockout mice and HEK293 overexpression","pmids":["41444608"],"confidence":"Medium","gaps":["Whether PRSS55 cleaves BCKDK/BCKDHA or acts as a non-catalytic scaffold is unresolved","Single lab study; BCKDK/BCKDHA interaction not independently replicated","How PRSS55 is dually localized to acrosome and mitochondria is unexplained"]},{"year":null,"claim":"Whether PRSS55 functions as an active serine protease or through non-catalytic mechanisms remains unknown; no proteolytic substrate has been identified, catalytic-dead mutants have not been tested, and the structural basis for ADAM3 stabilization and BCAA metabolic regulation is uncharacterized.","evidence":"","pmids":[],"confidence":"High","gaps":["No substrate identified for PRSS55 protease activity","Catalytic-dead mutant not tested in vivo","No structural model explaining PRSS55 interaction with BCKDK/BCKDHA or mechanism of ADAM3 stabilization"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["BCKDK","BCKDHA","ADAM3"],"other_free_text":[]},"mechanistic_narrative":"PRSS55 is a testis-specific, GPI-anchored chymotrypsin-like serine protease essential for male fertility that functions in sperm maturation, migration through the uterotubal junction, and zona pellucida binding. It contains a catalytic triad (His108, Asp156, Ser250) and localizes to the sperm acrosome and mitochondria; during epididymal maturation it stabilizes ADAM3 protein on sperm, though without direct physical interaction, and its loss abolishes ADAM3 from mature spermatozoa and impairs sperm-egg recognition [PMID:30032357, PMID:32301961]. PRSS55 also localizes to mitochondria where it physically interacts with BCKDK and BCKDHA to regulate branched-chain amino acid catabolism and mitochondrial energy production; its absence causes BCAA accumulation, decreased ATP content, reduced mitochondrial membrane potential, and structural defects in mitochondrial cristae and axonemal microtubules [PMID:41444608, PMID:33417308]. A homozygous missense mutation (p.A192V) in human PRSS55 causes male infertility with teratozoospermia [PMID:35821214]."},"prefetch_data":{"uniprot":{"accession":"Q6UWB4","full_name":"Serine protease 55","aliases":["Testis serine protease 1","T-SP1"],"length_aa":352,"mass_kda":38.9,"function":"Probable serine protease, which plays a crucial role in the fertility of male mice including sperm migration and sperm-egg interaction","subcellular_location":"Cytoplasm, cytosol","url":"https://www.uniprot.org/uniprotkb/Q6UWB4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PRSS55","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/PRSS55","total_profiled":1310},"omim":[{"mim_id":"619676","title":"SPERM MICROTUBULE INNER PROTEIN 9; SPMIP9","url":"https://www.omim.org/entry/619676"},{"mim_id":"615144","title":"PROTEASE, SERINE, 55; PRSS55","url":"https://www.omim.org/entry/615144"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Acrosome","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in single","driving_tissues":[{"tissue":"testis","ntpm":26.0}],"url":"https://www.proteinatlas.org/search/PRSS55"},"hgnc":{"alias_symbol":["T-SP1","UNQ9391","CT153"],"prev_symbol":[]},"alphafold":{"accession":"Q6UWB4","domains":[{"cath_id":"2.40.10.10","chopping":"81-175_293-308","consensus_level":"medium","plddt":94.7409,"start":81,"end":308},{"cath_id":"2.40.10.10","chopping":"184-289","consensus_level":"medium","plddt":81.7251,"start":184,"end":289}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UWB4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UWB4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UWB4-F1-predicted_aligned_error_v6.png","plddt_mean":75.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PRSS55","jax_strain_url":"https://www.jax.org/strain/search?query=PRSS55"},"sequence":{"accession":"Q6UWB4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UWB4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UWB4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UWB4"}},"corpus_meta":[{"pmid":"30032357","id":"PMC_30032357","title":"Serine protease PRSS55 is crucial for male mouse fertility via affecting sperm migration and sperm-egg binding.","date":"2018","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/30032357","citation_count":53,"is_preprint":false},{"pmid":"29563520","id":"PMC_29563520","title":"The evolutionarily conserved genes: Tex37, Ccdc73, Prss55 and Nxt2 are dispensable for fertility in mice.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29563520","citation_count":41,"is_preprint":false},{"pmid":"20351143","id":"PMC_20351143","title":"Biological characterization of Chlamydia trachomatis plasticity zone MACPF domain family protein CT153.","date":"2010","source":"Infection and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/20351143","citation_count":31,"is_preprint":false},{"pmid":"32301961","id":"PMC_32301961","title":"Prss55 but not Prss51 is required for male fertility in mice†.","date":"2020","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/32301961","citation_count":29,"is_preprint":false},{"pmid":"33417308","id":"PMC_33417308","title":"PRSS55 plays an important role in the structural differentiation and energy metabolism of sperm and is required for male fertility in mice.","date":"2021","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33417308","citation_count":25,"is_preprint":false},{"pmid":"35821214","id":"PMC_35821214","title":"PRSS55 is a novel potential causative gene for human male infertility.","date":"2022","source":"Reproductive biomedicine online","url":"https://pubmed.ncbi.nlm.nih.gov/35821214","citation_count":6,"is_preprint":false},{"pmid":"32850029","id":"PMC_32850029","title":"COLIA1 + 1245 G > T Sp1 Binding Site Polymorphism is Not Associated with ACL Injury Risks Among Indian Athletes.","date":"2020","source":"Indian journal of orthopaedics","url":"https://pubmed.ncbi.nlm.nih.gov/32850029","citation_count":6,"is_preprint":false},{"pmid":"18844450","id":"PMC_18844450","title":"T-SP1: a novel serine protease-like protein predominantly expressed in testis.","date":"2008","source":"Biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18844450","citation_count":5,"is_preprint":false},{"pmid":"24798016","id":"PMC_24798016","title":"Chlamydial MACPF protein CT153.","date":"2014","source":"Sub-cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24798016","citation_count":3,"is_preprint":false},{"pmid":"40764777","id":"PMC_40764777","title":"Rescue of male infertility by human PRSS55 in transgenic mice establishes a contraceptive research model.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40764777","citation_count":1,"is_preprint":false},{"pmid":"41444608","id":"PMC_41444608","title":"PRSS55 regulates BCAA metabolism and interacts with BCKDK and BCKDHA in mouse testes and sperm.","date":"2025","source":"Cell & bioscience","url":"https://pubmed.ncbi.nlm.nih.gov/41444608","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6985,"output_tokens":2071,"usd":0.02601},"stage2":{"model":"claude-opus-4-6","input_tokens":5328,"output_tokens":2062,"usd":0.117285},"total_usd":0.143295,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2018,\n      \"finding\": \"PRSS55 is a GPI-anchored membrane protein specifically expressed in adult mouse testis, localized to the luminal side of seminiferous tubules and sperm acrosome. Knockout of Prss55 results in impaired in vivo sperm migration from uterus to oviduct and defective sperm-egg recognition/binding to zona-intact and zona-free oocytes. Mature ADAM3 is almost undetectable in Prss55-/- sperm (precursor ADAM3 is unchanged in testis), though ADAM3 does not directly interact with PRSS55 by co-immunoprecipitation.\",\n      \"method\": \"Knockout mice (Prss55-/-), in vivo/in vitro fertilization assays, immunoprecipitation, immunofluorescence, microarray analysis\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple defined phenotypic readouts, GPI-anchor localization, ADAM3 maturation assay; replicated by independent labs\",\n      \"pmids\": [\"30032357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PRSS55, but not its paralog PRSS51, is required for male fertility in mice. Prss55 KO mice phenocopy double-KO mice, showing impaired sperm migration through the uterotubal junction (UTJ) and impaired sperm-zona pellucida (ZP) binding. ADAM3 protein is lost from Prss55-/- epididymal spermatozoa, indicating PRSS55 stabilizes ADAM3 during epididymal maturation for efficient UTJ migration and ZP binding.\",\n      \"method\": \"CRISPR/Cas9 single and double knockout mice, fertility trials, sperm migration assays, zona pellucida binding assays, western blot for ADAM3\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via single vs. double KO, multiple orthogonal functional assays, independent replication of ADAM3 loss\",\n      \"pmids\": [\"32301961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Deletion of all Prss55 transcripts leads to sperm structural abnormalities including deficient '9+2' microtubule arrangement, damaged peripheral dense fibers, and defective mitochondrial cristae. Prss55-/- sperm show decreased expression of electron transport chain molecules and lower ATP content. PRSS55 may function by activating type II muscle myosin in the testis, involved in cytoskeleton translocation.\",\n      \"method\": \"Knockout mice targeting all transcripts, transmission electron microscopy, ATP measurement, proteomics/western blot for ETC molecules\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO with structural and metabolic phenotypic readouts, but myosin activation is preliminary/speculative\",\n      \"pmids\": [\"33417308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human PRSS55 (described as T-SP1) is a membrane-anchored chymotrypsin (S1)-like serine protease encoded on chromosome 8p with a catalytic triad of His108, Asp156, and Ser250. Alternative splicing generates three variants; only the T-SP1/1 variant contains a C-terminal hydrophobic domain enabling GPI/membrane anchoring. The protein is expressed in Leydig and Sertoli cells of testis and in epithelial cells of ductuli efferentes.\",\n      \"method\": \"RACE, sequencing, domain analysis, polyclonal antibody immunohistochemistry\",\n      \"journal\": \"Biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical characterization of domain architecture and catalytic triad, localization by IHC with specific antibody\",\n      \"pmids\": [\"18844450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Human PRSS55 expressed transgenically in Prss55 null mice can functionally rescue male fertility, with the intracellularly-tagged version (RES TM) restoring fertility to levels comparable to wild-type controls, validating functional conservation of human PRSS55. The extracellularly-tagged version (RES GPI) only partially restored fertility, indicating the C-terminal tag position (and thus membrane orientation) affects function.\",\n      \"method\": \"Transgenic rescue in Prss55-/- mice, continuous mating fertility trials, sperm parameter analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transgenic rescue with functional readout; single lab study\",\n      \"pmids\": [\"40764777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PRSS55 is localized to mitochondria in sperm (validated by immunofluorescence in sperm and transfected NIH-3T3 cells, and immunoblotting of testis and HEK293 cells). Prss55-/- testes and sperm show impaired mitochondrial function including low ATP production and decreased mitochondrial membrane potential. Overexpression of PRSS55 in HEK293 cells increases ATP production and NAD+/NADH ratio. By proteomics and metabolomics, PRSS55 loss leads to accumulation of branched-chain amino acids (BCAAs: valine, leucine, isoleucine) in testes. Co-IP and LC-MS/MS validated that PRSS55 physically interacts with BCKDK (branched-chain alpha-ketoacid dehydrogenase kinase) and BCKDHA (branched-chain ketoacid dehydrogenase E1α), two key enzymes of BCAA catabolism.\",\n      \"method\": \"Immunofluorescence, immunoblotting, subcellular fractionation, overexpression in HEK293 cells (ATP/NAD+ assays), proteomics, metabolomics, Co-IP, LC-MS/MS\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, LC-MS/MS, metabolomics, in vitro overexpression assay), single lab study\",\n      \"pmids\": [\"41444608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A homozygous missense mutation in human PRSS55 (c.575C>T, p.A192V) causes male infertility with teratozoospermia. The mutation alters PRSS55 protein conformation and causes a sharp decrease in PRSS55 protein levels in patient spermatozoa, as demonstrated by immunofluorescence and western blot. PRSS55 localizes to the head and flagella of human spermatids and epididymal spermatozoa.\",\n      \"method\": \"Whole exome sequencing, Sanger sequencing, western blot, immunofluorescence, electron microscopy\",\n      \"journal\": \"Reproductive biomedicine online\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — human patient variant with protein-level validation; single case\",\n      \"pmids\": [\"35821214\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PRSS55 is a testis-specific, GPI-anchored chymotrypsin-like serine protease that localizes to the sperm acrosome and mitochondria, where it stabilizes ADAM3 protein during epididymal maturation to enable sperm migration through the uterotubal junction and zona pellucida binding, and additionally interacts with BCKDK and BCKDHA to regulate branched-chain amino acid metabolism and mitochondrial energy production in sperm.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PRSS55 is a testis-specific, GPI-anchored chymotrypsin-like serine protease essential for male fertility that functions in sperm maturation, migration through the uterotubal junction, and zona pellucida binding. It contains a catalytic triad (His108, Asp156, Ser250) and localizes to the sperm acrosome and mitochondria; during epididymal maturation it stabilizes ADAM3 protein on sperm, though without direct physical interaction, and its loss abolishes ADAM3 from mature spermatozoa and impairs sperm-egg recognition [PMID:30032357, PMID:32301961]. PRSS55 also localizes to mitochondria where it physically interacts with BCKDK and BCKDHA to regulate branched-chain amino acid catabolism and mitochondrial energy production; its absence causes BCAA accumulation, decreased ATP content, reduced mitochondrial membrane potential, and structural defects in mitochondrial cristae and axonemal microtubules [PMID:41444608, PMID:33417308]. A homozygous missense mutation (p.A192V) in human PRSS55 causes male infertility with teratozoospermia [PMID:35821214].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Initial molecular characterization established that PRSS55 is a membrane-anchored S1-family serine protease with a complete catalytic triad and GPI-anchoring capability, resolving its domain architecture and testicular cell-type expression.\",\n      \"evidence\": \"RACE cloning, domain analysis, and immunohistochemistry on human testis\",\n      \"pmids\": [\"18844450\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No enzymatic activity or substrate demonstrated\",\n        \"Functional role in reproduction not yet tested\",\n        \"GPI-anchoring not confirmed biochemically (inferred from hydrophobic domain)\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Knockout studies revealed that PRSS55 is required for sperm migration from uterus to oviduct and for sperm-zona pellucida binding, and that it controls ADAM3 maturation on epididymal sperm without direct physical interaction with ADAM3.\",\n      \"evidence\": \"Prss55-/- knockout mice with in vivo/in vitro fertilization assays, co-immunoprecipitation, immunofluorescence\",\n      \"pmids\": [\"30032357\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which PRSS55 stabilizes ADAM3 indirectly remains unknown\",\n        \"No proteolytic substrate identified\",\n        \"Whether catalytic activity is required for function not tested\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Genetic epistasis analysis demonstrated that PRSS55, but not its paralog PRSS51, is the functionally relevant protease for UTJ migration and ZP binding, independently confirming ADAM3 loss as a key downstream consequence.\",\n      \"evidence\": \"CRISPR/Cas9 single and double knockout mice with fertility trials and sperm migration assays\",\n      \"pmids\": [\"32301961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether PRSS55 acts enzymatically or as a scaffold/chaperone is unresolved\",\n        \"Downstream signaling between PRSS55 loss and ADAM3 destabilization not mapped\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Complete deletion of Prss55 transcripts revealed sperm ultrastructural defects (disrupted 9+2 axoneme, damaged dense fibers, defective mitochondrial cristae) and decreased ATP, expanding the functional role beyond ADAM3 to mitochondrial and cytoskeletal integrity.\",\n      \"evidence\": \"Knockout mice with transmission electron microscopy, ATP measurement, and proteomics\",\n      \"pmids\": [\"33417308\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Proposed myosin activation mechanism is preliminary and not validated by direct interaction or activity assays\",\n        \"Relationship between mitochondrial defects and ADAM3 loss not clarified\",\n        \"Whether structural defects are primary or secondary to metabolic dysfunction is unclear\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of a human PRSS55 missense variant (p.A192V) causing teratozoospermia established PRSS55 as a human male infertility gene and demonstrated that protein stability is critical for function.\",\n      \"evidence\": \"Whole exome sequencing of infertile patient, protein-level validation by western blot and immunofluorescence\",\n      \"pmids\": [\"35821214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single family reported; replication in independent cohorts needed\",\n        \"Whether p.A192V disrupts catalytic activity versus protein folding not distinguished\",\n        \"No functional rescue experiment performed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Transgenic rescue with human PRSS55 confirmed functional conservation across species and showed that C-terminal membrane orientation (intracellular vs. extracellular tag) critically affects fertility restoration.\",\n      \"evidence\": \"Transgenic rescue in Prss55-/- mice with continuous mating fertility trials\",\n      \"pmids\": [\"40764777\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether partial rescue by GPI-tagged version reflects impaired trafficking, folding, or activity is unknown\",\n        \"Single lab study without independent replication\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mitochondrial localization and physical interaction with BCKDK and BCKDHA linked PRSS55 to branched-chain amino acid catabolism and mitochondrial energy production, providing a mechanistic basis for the ATP deficiency observed in knockout sperm.\",\n      \"evidence\": \"Co-IP, LC-MS/MS, metabolomics, ATP and NAD+ assays in knockout mice and HEK293 overexpression\",\n      \"pmids\": [\"41444608\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether PRSS55 cleaves BCKDK/BCKDHA or acts as a non-catalytic scaffold is unresolved\",\n        \"Single lab study; BCKDK/BCKDHA interaction not independently replicated\",\n        \"How PRSS55 is dually localized to acrosome and mitochondria is unexplained\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether PRSS55 functions as an active serine protease or through non-catalytic mechanisms remains unknown; no proteolytic substrate has been identified, catalytic-dead mutants have not been tested, and the structural basis for ADAM3 stabilization and BCAA metabolic regulation is uncharacterized.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No substrate identified for PRSS55 protease activity\",\n        \"Catalytic-dead mutant not tested in vivo\",\n        \"No structural model explaining PRSS55 interaction with BCKDK/BCKDHA or mechanism of ADAM3 stabilization\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"BCKDK\",\n      \"BCKDHA\",\n      \"ADAM3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}