{"gene":"PCCB","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1986,"finding":"PCCB encodes the beta subunit of propionyl-CoA carboxylase (PCC), a biotin-dependent enzyme (EC 6.4.1.3) that catalyzes carboxylation of propionyl-CoA; the beta-chain cDNA was isolated and confirmed to encode beta-PCC by peptide sequence matching, and the PCCB gene was chromosomally assigned to chromosome 3 by somatic cell hybrid analysis.","method":"cDNA cloning, oligonucleotide probing, peptide sequencing, somatic cell hybrid panel blot hybridization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical identification of encoded polypeptide via peptide sequencing plus cDNA cloning; foundational characterization replicated in subsequent studies","pmids":["3460076"],"is_preprint":false},{"year":1993,"finding":"The beta-PCC precursor cDNA encodes a polypeptide of 539 amino acids (molecular mass ~58,202 Da) sharing 91% amino acid identity with rat beta-PCC; an 8-bp intronic deletion disrupts the 5' splice signal, causing exon skipping in a PA patient, establishing that splicing mutations in PCCB can abolish functional enzyme.","method":"cDNA cloning, sequencing of RT-PCR products, genomic DNA PCR sequencing","journal":"Human genetics","confidence":"High","confidence_rationale":"Tier 1 / Strong — full-length cDNA sequencing with functional splice defect confirmed at both mRNA and genomic DNA levels; consistent with broader corpus","pmids":["8225321"],"is_preprint":false},{"year":1999,"finding":"PCC is a dodecameric heteropolymeric mitochondrial enzyme composed of alpha (PCCA-encoded) and beta (PCCB-encoded) subunits; PCCB mutations cause loss of beta-PCC subunit detectable by Western blot, while many PCCA mutations lead to combined absence of both subunits, establishing distinct subunit-stability dependencies.","method":"Western blot, complementation assay, Northern blot, RT-PCR sequencing","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods (Western blot, Northern blot, complementation) across multiple patient cell lines in a systematic review of mutations","pmids":["10502773"],"is_preprint":false},{"year":2001,"finding":"Mutations in the C-terminal region of PCCB (R512C, L519P, W531X, N536D) directly inhibit alpha-beta heteromeric and/or beta-beta homomeric assembly of PCC at both normal and reduced temperatures, indicating a primary structural role of the C-terminus in subunit assembly; N-terminal mutations (R67S, S106R, G131D, R165W, E168K, G198D) impair assembly only at elevated temperature, suggesting they act as folding defects that indirectly disrupt assembly.","method":"Mammalian two-hybrid system assay at two temperatures, site-directed mutagenesis","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 1 / Moderate — two-hybrid interaction assay with temperature-shift to discriminate direct assembly vs. folding defects; 12 mutations systematically analyzed, single lab with multiple orthogonal conditions","pmids":["11749052"],"is_preprint":false},{"year":2003,"finding":"Expression of 18 PCCB missense variants in PCCB-deficient human fibroblasts showed: L17M and A497V substitutions retain wild-type PCC activity (non-pathogenic); K218R, R410W and N536D retain substantial residual activity; 13 others show null/very low activity; L519P, R512C and G112D mutations cause beta-PCC protein instability by Western blot, establishing that most PCCB pathogenic variants abolish activity with a subset also destabilizing the protein.","method":"Transient transfection of PCCB-deficient fibroblasts, PCC enzyme activity assay, Western blot protein stability analysis","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct functional reconstitution in the physiological cellular context with enzyme activity assay and protein stability readout for 18 variants in a single systematic study","pmids":["12757933"],"is_preprint":false},{"year":2017,"finding":"Deletion of the C. elegans pccb-1 gene (ortholog of PCCB) globally impairs mitochondrial oxidative phosphorylation capacity and efficiency (measured by direct polarography of isolated mitochondria), inhibits distal TCA cycle flux (reduced +1 malate by GC/MS with 13C-glucose), and reduces animal lifespan, establishing that PCCB/pccb-1 loss disrupts mitochondrial energy metabolism beyond simple propionyl-CoA accumulation.","method":"Genetic deletion, direct polarography of isolated mitochondria, GC/MS isotopic flux analysis with 13C-glucose, lifespan assay, UPLC amino acid profiling","journal":"Journal of inherited metabolic disease","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal metabolic readouts (polarography, isotope tracing, lifespan) in a defined genetic deletion model; single lab but rigorous multi-method study","pmids":["29159707"],"is_preprint":false},{"year":2023,"finding":"PCCB knockdown in human forebrain organoids reduces TCA cycle activity, resulting in decreased GABA levels (confirmed by metabolomics), and dysregulates GABAergic synapse gene networks; multielectrode array recording showed PCCB-knockdown organoids exhibit hyper-neuroactivity and decreased neural network synchronization, establishing a functional link between PCCB-dependent mitochondrial metabolism and GABAergic pathway activity.","method":"shRNA knockdown in human forebrain organoids, RNA sequencing, metabolomics, mitochondrial function assays, multielectrode array recording","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal readouts (transcriptomics, metabolomics, electrophysiology) in a single lab; mechanistic link is correlative via knockdown rather than direct reconstitution","pmids":["37620341"],"is_preprint":false},{"year":2024,"finding":"PPDPF protein interacts with PCCA (the alpha subunit of PCC) as identified by mass spectrometry, and PPDPF inhibits the interaction between PCCA and PCCB, thereby suppressing PCC-mediated methionine catabolism and elevating methionine and SAM levels in esophageal squamous cell carcinoma cells.","method":"Mass spectrometry interaction screen, co-immunoprecipitation (implied by interaction identification), PPDPF knockdown metabolomics","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — mass spectrometry interaction and knockdown metabolomics from a single study; interaction between PPDPF and PCCA is established but the mechanism of PCCB displacement is inferred rather than directly demonstrated by reconstitution","pmids":["39694223"],"is_preprint":false},{"year":2023,"finding":"Two novel PCCB missense/deletion variants (p.G246del and p.S322F) identified in cis in a PA patient each individually reduce PCC enzyme activity and/or beta-PCC protein levels when expressed in a eukaryotic system; the double mutant shows no residual PCC activity, confirming both variants are pathogenic loss-of-function changes affecting protein stability or catalytic function.","method":"Eukaryotic expression system, PCC enzyme activity assay, Western blot for protein levels","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct enzyme activity reconstitution assay with protein stability readout, but single lab, two novel variants only","pmids":["37839763"],"is_preprint":false}],"current_model":"PCCB encodes the beta subunit of mitochondrial propionyl-CoA carboxylase (PCC), a dodecameric biotin-dependent enzyme that carboxylates propionyl-CoA to methylmalonyl-CoA; the beta subunit assembles with alpha subunits (PCCA) through interactions mediated by its C-terminal domain (required for heteromeric α-β and homomeric β-β assembly) and N-terminal domain (required for proper folding), and loss of PCCB function globally disrupts TCA cycle flux and mitochondrial oxidative phosphorylation, with emerging evidence that PCCB-dependent mitochondrial metabolism also regulates GABAergic neurotransmitter levels, and that PPDPF can block PCCA-PCCB interaction to suppress PCC activity and methionine catabolism."},"narrative":{"mechanistic_narrative":"PCCB encodes the beta subunit of mitochondrial propionyl-CoA carboxylase (PCC), a biotin-dependent enzyme (EC 6.4.1.3) that carboxylates propionyl-CoA to methylmalonyl-CoA and which assembles as a dodecameric heteropolymer of alpha (PCCA) and beta (PCCB) subunits [PMID:3460076, PMID:10502773]. Within this assembly, the beta subunit's C-terminal region mediates both alpha-beta heteromeric and beta-beta homomeric contacts, while N-terminal regions are required for proper folding, so that C-terminal mutations directly abolish assembly whereas N-terminal substitutions act as temperature-sensitive folding defects [PMID:11749052]. The great majority of pathogenic PCCB variants abolish catalytic activity, and a subset additionally destabilizes the beta-PCC protein, providing the molecular basis for propionic acidemia [PMID:12757933, PMID:37839763]. Beyond propionyl-CoA accumulation, loss of PCCB function globally impairs mitochondrial oxidative phosphorylation and constrains distal TCA cycle flux [PMID:29159707], and PCCB-dependent metabolism feeds GABAergic neurotransmission, since PCCB knockdown lowers GABA levels and dysregulates GABAergic synapse networks with consequent neuronal hyperactivity [PMID:37620341]. PCC activity is further regulated by PPDPF, which binds PCCA and blocks the PCCA-PCCB interaction to suppress PCC-mediated methionine catabolism [PMID:39694223].","teleology":[{"year":1986,"claim":"Established the molecular identity of the PCCB gene product, answering what polypeptide PCCB encodes and where it maps in the genome.","evidence":"cDNA cloning with peptide sequence matching and somatic cell hybrid chromosomal assignment","pmids":["3460076"],"confidence":"High","gaps":["No information on subunit stoichiometry or assembly","Catalytic mechanism not addressed beyond EC assignment"]},{"year":1993,"claim":"Defined the full-length beta-PCC precursor sequence and demonstrated that splicing mutations abolish functional enzyme, linking PCCB lesions to propionic acidemia at the mRNA and genomic level.","evidence":"Full-length cDNA cloning and sequencing of RT-PCR and genomic DNA products from a PA patient","pmids":["8225321"],"confidence":"High","gaps":["Single patient splice defect; spectrum of mutation types not surveyed","No structural mapping of the encoded protein"]},{"year":1999,"claim":"Showed that PCC is a dodecameric alpha-beta heteropolymer and that PCCB versus PCCA mutations differ in their effects on subunit stability, establishing distinct subunit interdependencies.","evidence":"Western blot, Northern blot, complementation across patient cell lines","pmids":["10502773"],"confidence":"High","gaps":["Which protein domains mediate assembly not yet mapped","Mechanism of differential subunit stability unresolved"]},{"year":2001,"claim":"Localized the assembly determinants within the beta subunit, distinguishing C-terminal mutations that directly block assembly from N-terminal mutations acting as folding defects.","evidence":"Mammalian two-hybrid assay at two temperatures with site-directed mutants","pmids":["11749052"],"confidence":"High","gaps":["No atomic structure of the assembly interface","Two-hybrid readout is indirect for in vivo dodecamer formation"]},{"year":2003,"claim":"Distinguished catalytic loss from protein-instability mechanisms across many PCCB variants, refining genotype-to-mechanism interpretation.","evidence":"Transient expression of 18 variants in PCCB-deficient fibroblasts with activity and stability readouts","pmids":["12757933"],"confidence":"High","gaps":["Does not resolve structural basis of catalytic loss for individual residues","Folding/degradation pathway not defined"]},{"year":2017,"claim":"Demonstrated that PCCB loss disrupts mitochondrial energy metabolism broadly, beyond simple propionyl-CoA accumulation, including OXPHOS capacity and distal TCA flux.","evidence":"Genetic deletion of C. elegans pccb-1 with polarography, 13C-glucose GC/MS flux analysis, and lifespan assays","pmids":["29159707"],"confidence":"High","gaps":["Ortholog model; human relevance inferred","Mechanism linking propionyl-CoA buildup to TCA inhibition not directly traced"]},{"year":2023,"claim":"Connected PCCB-dependent mitochondrial metabolism to GABAergic neurotransmission and neural network activity, offering a mechanistic basis for neurological phenotypes.","evidence":"shRNA knockdown in human forebrain organoids with RNA-seq, metabolomics, mitochondrial assays, and multielectrode array recording","pmids":["37620341"],"confidence":"Medium","gaps":["Link is correlative via knockdown rather than reconstitution","Causal step from TCA flux to GABA synthesis not isolated"]},{"year":2023,"claim":"Validated additional novel PCCB variants as loss-of-function via direct reconstitution, supporting clinical interpretation of compound lesions.","evidence":"Eukaryotic expression of p.G246del and p.S322F with PCC activity and Western blot stability readouts","pmids":["37839763"],"confidence":"Medium","gaps":["Single lab, only two variants","Structural impact on the enzyme not modeled"]},{"year":2024,"claim":"Identified a regulatory mechanism controlling PCC activity, showing PPDPF binds PCCA and blocks PCCA-PCCB interaction to suppress methionine catabolism.","evidence":"Mass spectrometry interaction screen and PPDPF knockdown metabolomics in esophageal squamous cell carcinoma cells","pmids":["39694223"],"confidence":"Medium","gaps":["Mechanism of PCCB displacement inferred, not shown by reconstitution","PPDPF binds PCCA; direct PCCB contact not demonstrated"]},{"year":null,"claim":"The atomic structure of the assembled human PCC dodecamer and the precise residue-level basis by which beta-subunit mutations and PPDPF regulate alpha-beta assembly remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of the assembly interface in the corpus","Direct biochemical reconstitution of PPDPF-mediated disassembly absent"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,4,8]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,5]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,7]}],"complexes":["propionyl-CoA carboxylase (PCC)"],"partners":["PCCA","PPDPF"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P05166","full_name":"Propionyl-CoA carboxylase beta chain, mitochondrial","aliases":["Propanoyl-CoA:carbon dioxide ligase subunit beta"],"length_aa":539,"mass_kda":58.2,"function":"This is one of the 2 subunits of the biotin-dependent propionyl-CoA carboxylase (PCC), a mitochondrial enzyme involved in the catabolism of odd chain fatty acids, branched-chain amino acids isoleucine, threonine, methionine, and valine and other metabolites (PubMed:15890657, PubMed:6765947). Propionyl-CoA carboxylase catalyzes the carboxylation of propionyl-CoA/propanoyl-CoA to D-methylmalonyl-CoA/(S)-methylmalonyl-CoA (PubMed:15890657, PubMed:6765947). Within the holoenzyme, the alpha subunit catalyzes the ATP-dependent carboxylation of the biotin carried by the biotin carboxyl carrier (BCC) domain, while the beta subunit then transfers the carboxyl group from carboxylated biotin to propionyl-CoA (By similarity). Propionyl-CoA carboxylase also significantly acts on butyryl-CoA/butanoyl-CoA, which is converted to ethylmalonyl-CoA/(2S)-ethylmalonyl-CoA at a much lower rate (PubMed:6765947). Other alternative minor substrates include (2E)-butenoyl-CoA/crotonoyl-CoA (By similarity)","subcellular_location":"Mitochondrion matrix","url":"https://www.uniprot.org/uniprotkb/P05166/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PCCB","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PCCB","total_profiled":1310},"omim":[{"mim_id":"617635","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, AUTOSOMAL DOMINANT 47; MRD47","url":"https://www.omim.org/entry/617635"},{"mim_id":"610422","title":"ALOPECIA-INTELLECTUAL DISABILITY SYNDROME 2; APMR2","url":"https://www.omim.org/entry/610422"},{"mim_id":"609058","title":"METHYLMALONYL-CoA MUTASE; MMUT","url":"https://www.omim.org/entry/609058"},{"mim_id":"606054","title":"PROPIONIC ACIDEMIA","url":"https://www.omim.org/entry/606054"},{"mim_id":"232050","title":"PROPIONYL-CoA CARBOXYLASE, BETA SUBUNIT; PCCB","url":"https://www.omim.org/entry/232050"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"liver","ntpm":188.7}],"url":"https://www.proteinatlas.org/search/PCCB"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P05166","domains":[{"cath_id":"3.90.226.10","chopping":"50-277","consensus_level":"high","plddt":97.473,"start":50,"end":277},{"cath_id":"3.90.226.10","chopping":"301-459_503-523","consensus_level":"high","plddt":97.5465,"start":301,"end":523}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P05166","model_url":"https://alphafold.ebi.ac.uk/files/AF-P05166-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P05166-F1-predicted_aligned_error_v6.png","plddt_mean":93.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PCCB","jax_strain_url":"https://www.jax.org/strain/search?query=PCCB"},"sequence":{"accession":"P05166","fasta_url":"https://rest.uniprot.org/uniprotkb/P05166.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P05166/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P05166"}},"corpus_meta":[{"pmid":"3460076","id":"PMC_3460076","title":"Isolation of cDNA clones coding for the alpha and beta chains of human propionyl-CoA carboxylase: chromosomal assignments and DNA polymorphisms associated with PCCA and PCCB genes.","date":"1986","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/3460076","citation_count":110,"is_preprint":false},{"pmid":"10502773","id":"PMC_10502773","title":"Overview of mutations in the PCCA and PCCB genes causing propionic acidemia.","date":"1999","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/10502773","citation_count":70,"is_preprint":false},{"pmid":"37620341","id":"PMC_37620341","title":"Human forebrain organoid-based multi-omics analyses of PCCB as a schizophrenia associated gene linked to GABAergic pathways.","date":"2023","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/37620341","citation_count":34,"is_preprint":false},{"pmid":"15059621","id":"PMC_15059621","title":"Mutation spectrum of the PCCA and PCCB genes in Japanese patients with propionic acidemia.","date":"2004","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/15059621","citation_count":31,"is_preprint":false},{"pmid":"12757933","id":"PMC_12757933","title":"Functional analysis of PCCB mutations causing propionic acidemia based on expression studies in deficient human skin fibroblasts.","date":"2003","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/12757933","citation_count":30,"is_preprint":false},{"pmid":"2249848","id":"PMC_2249848","title":"Two distinct mutations at the same site in the PCCB gene in propionic acidemia.","date":"1990","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/2249848","citation_count":27,"is_preprint":false},{"pmid":"8411997","id":"PMC_8411997","title":"Three independent mutations in the same exon of the PCCB gene: differences between Caucasian and Japanese propionic acidaemia.","date":"1993","source":"Journal of inherited metabolic disease","url":"https://pubmed.ncbi.nlm.nih.gov/8411997","citation_count":24,"is_preprint":false},{"pmid":"11749052","id":"PMC_11749052","title":"Effect of PCCB gene mutations on the heteromeric and homomeric assembly of propionyl-CoA carboxylase.","date":"2001","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/11749052","citation_count":21,"is_preprint":false},{"pmid":"8225321","id":"PMC_8225321","title":"The molecular defect in propionic acidemia: exon skipping caused by an 8-bp deletion from an intron in the PCCB allele.","date":"1993","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8225321","citation_count":18,"is_preprint":false},{"pmid":"29159707","id":"PMC_29159707","title":"Propionyl-CoA carboxylase pcca-1 and pccb-1 gene deletions in Caenorhabditis elegans globally impair mitochondrial energy metabolism.","date":"2017","source":"Journal of inherited metabolic 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Mutation in brief no. 253. 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international journal of clinical chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/33798502","citation_count":3,"is_preprint":false},{"pmid":"27081542","id":"PMC_27081542","title":"A novel PCCB mutation in a Thai patient with propionic acidemia identified by exome sequencing.","date":"2015","source":"Human genome variation","url":"https://pubmed.ncbi.nlm.nih.gov/27081542","citation_count":3,"is_preprint":false},{"pmid":"33127324","id":"PMC_33127324","title":"Biochemical phenotype and its relationship to treatment in 16 individuals with PCCB c.1606A > G (p.Asn536Asp) variant propionic acidemia.","date":"2020","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/33127324","citation_count":3,"is_preprint":false},{"pmid":"32252659","id":"PMC_32252659","title":"Case reports: three novel variants in PCCA and PCCB genes in Chinese patients with propionic acidemia.","date":"2020","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32252659","citation_count":3,"is_preprint":false},{"pmid":"37776842","id":"PMC_37776842","title":"A common benign intronic deletion masking a pathogenic deep intronic PCCB variant - genome sequencing and RNA studies to the rescue.","date":"2023","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/37776842","citation_count":2,"is_preprint":false},{"pmid":"40044943","id":"PMC_40044943","title":"Novel CRISPR-Cas9 iPSC knockouts for PCCA and PCCB genes: advancing propionic acidemia research.","date":"2025","source":"Human cell","url":"https://pubmed.ncbi.nlm.nih.gov/40044943","citation_count":1,"is_preprint":false},{"pmid":"37034773","id":"PMC_37034773","title":"Human forebrain organoids-based multi-omics analyses reveal PCCB's regulation on GABAergic system contributing to schizophrenia.","date":"2023","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/37034773","citation_count":1,"is_preprint":false},{"pmid":"32822967","id":"PMC_32822967","title":"Generation of isogenic Propionyl-CoA carboxylase beta subunit (PCCB) deficient induced pluripotent stem cell lines.","date":"2020","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/32822967","citation_count":1,"is_preprint":false},{"pmid":"37839763","id":"PMC_37839763","title":"Functional analysis of novel variants identified in cis in the PCCB gene in a patient with propionic acidemia.","date":"2023","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/37839763","citation_count":1,"is_preprint":false},{"pmid":"33751535","id":"PMC_33751535","title":"[Identification of two novel variants of the PCCB gene in a pedigree affected with propionic acidemia].","date":"2021","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33751535","citation_count":1,"is_preprint":false},{"pmid":"39694223","id":"PMC_39694223","title":"PPDPF promotes esophageal squamous cell carcinoma progression by blocking PCCA binding to PCCB and inhibiting methionine catabolism.","date":"2024","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/39694223","citation_count":0,"is_preprint":false},{"pmid":"38394970","id":"PMC_38394970","title":"Establishment of a non-integrated iPSC line (SDQLCHi043-A) from a male infant with propionic acidemia carrying compound heterozygote mutations in PCCB gene.","date":"2024","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/38394970","citation_count":0,"is_preprint":false},{"pmid":"41776507","id":"PMC_41776507","title":"Identification of novel compound heterozygote variants in the PCCB gene in a fetus with undetectable fetal phenotype.","date":"2026","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/41776507","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.11.25329423","title":"The long non-coding RNA<i>TRIB1AL</i>links metabolic dysfunction-associated steatotic liver disease, cardiometabolic risk and human lifespan","date":"2025-06-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.11.25329423","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18281,"output_tokens":2488,"usd":0.046081,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9747,"output_tokens":2823,"usd":0.059655,"stage2_stop_reason":"end_turn"},"total_usd":0.105736,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1986,\n      \"finding\": \"PCCB encodes the beta subunit of propionyl-CoA carboxylase (PCC), a biotin-dependent enzyme (EC 6.4.1.3) that catalyzes carboxylation of propionyl-CoA; the beta-chain cDNA was isolated and confirmed to encode beta-PCC by peptide sequence matching, and the PCCB gene was chromosomally assigned to chromosome 3 by somatic cell hybrid analysis.\",\n      \"method\": \"cDNA cloning, oligonucleotide probing, peptide sequencing, somatic cell hybrid panel blot hybridization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical identification of encoded polypeptide via peptide sequencing plus cDNA cloning; foundational characterization replicated in subsequent studies\",\n      \"pmids\": [\"3460076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"The beta-PCC precursor cDNA encodes a polypeptide of 539 amino acids (molecular mass ~58,202 Da) sharing 91% amino acid identity with rat beta-PCC; an 8-bp intronic deletion disrupts the 5' splice signal, causing exon skipping in a PA patient, establishing that splicing mutations in PCCB can abolish functional enzyme.\",\n      \"method\": \"cDNA cloning, sequencing of RT-PCR products, genomic DNA PCR sequencing\",\n      \"journal\": \"Human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — full-length cDNA sequencing with functional splice defect confirmed at both mRNA and genomic DNA levels; consistent with broader corpus\",\n      \"pmids\": [\"8225321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PCC is a dodecameric heteropolymeric mitochondrial enzyme composed of alpha (PCCA-encoded) and beta (PCCB-encoded) subunits; PCCB mutations cause loss of beta-PCC subunit detectable by Western blot, while many PCCA mutations lead to combined absence of both subunits, establishing distinct subunit-stability dependencies.\",\n      \"method\": \"Western blot, complementation assay, Northern blot, RT-PCR sequencing\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods (Western blot, Northern blot, complementation) across multiple patient cell lines in a systematic review of mutations\",\n      \"pmids\": [\"10502773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Mutations in the C-terminal region of PCCB (R512C, L519P, W531X, N536D) directly inhibit alpha-beta heteromeric and/or beta-beta homomeric assembly of PCC at both normal and reduced temperatures, indicating a primary structural role of the C-terminus in subunit assembly; N-terminal mutations (R67S, S106R, G131D, R165W, E168K, G198D) impair assembly only at elevated temperature, suggesting they act as folding defects that indirectly disrupt assembly.\",\n      \"method\": \"Mammalian two-hybrid system assay at two temperatures, site-directed mutagenesis\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — two-hybrid interaction assay with temperature-shift to discriminate direct assembly vs. folding defects; 12 mutations systematically analyzed, single lab with multiple orthogonal conditions\",\n      \"pmids\": [\"11749052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Expression of 18 PCCB missense variants in PCCB-deficient human fibroblasts showed: L17M and A497V substitutions retain wild-type PCC activity (non-pathogenic); K218R, R410W and N536D retain substantial residual activity; 13 others show null/very low activity; L519P, R512C and G112D mutations cause beta-PCC protein instability by Western blot, establishing that most PCCB pathogenic variants abolish activity with a subset also destabilizing the protein.\",\n      \"method\": \"Transient transfection of PCCB-deficient fibroblasts, PCC enzyme activity assay, Western blot protein stability analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct functional reconstitution in the physiological cellular context with enzyme activity assay and protein stability readout for 18 variants in a single systematic study\",\n      \"pmids\": [\"12757933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Deletion of the C. elegans pccb-1 gene (ortholog of PCCB) globally impairs mitochondrial oxidative phosphorylation capacity and efficiency (measured by direct polarography of isolated mitochondria), inhibits distal TCA cycle flux (reduced +1 malate by GC/MS with 13C-glucose), and reduces animal lifespan, establishing that PCCB/pccb-1 loss disrupts mitochondrial energy metabolism beyond simple propionyl-CoA accumulation.\",\n      \"method\": \"Genetic deletion, direct polarography of isolated mitochondria, GC/MS isotopic flux analysis with 13C-glucose, lifespan assay, UPLC amino acid profiling\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal metabolic readouts (polarography, isotope tracing, lifespan) in a defined genetic deletion model; single lab but rigorous multi-method study\",\n      \"pmids\": [\"29159707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PCCB knockdown in human forebrain organoids reduces TCA cycle activity, resulting in decreased GABA levels (confirmed by metabolomics), and dysregulates GABAergic synapse gene networks; multielectrode array recording showed PCCB-knockdown organoids exhibit hyper-neuroactivity and decreased neural network synchronization, establishing a functional link between PCCB-dependent mitochondrial metabolism and GABAergic pathway activity.\",\n      \"method\": \"shRNA knockdown in human forebrain organoids, RNA sequencing, metabolomics, mitochondrial function assays, multielectrode array recording\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal readouts (transcriptomics, metabolomics, electrophysiology) in a single lab; mechanistic link is correlative via knockdown rather than direct reconstitution\",\n      \"pmids\": [\"37620341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PPDPF protein interacts with PCCA (the alpha subunit of PCC) as identified by mass spectrometry, and PPDPF inhibits the interaction between PCCA and PCCB, thereby suppressing PCC-mediated methionine catabolism and elevating methionine and SAM levels in esophageal squamous cell carcinoma cells.\",\n      \"method\": \"Mass spectrometry interaction screen, co-immunoprecipitation (implied by interaction identification), PPDPF knockdown metabolomics\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — mass spectrometry interaction and knockdown metabolomics from a single study; interaction between PPDPF and PCCA is established but the mechanism of PCCB displacement is inferred rather than directly demonstrated by reconstitution\",\n      \"pmids\": [\"39694223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Two novel PCCB missense/deletion variants (p.G246del and p.S322F) identified in cis in a PA patient each individually reduce PCC enzyme activity and/or beta-PCC protein levels when expressed in a eukaryotic system; the double mutant shows no residual PCC activity, confirming both variants are pathogenic loss-of-function changes affecting protein stability or catalytic function.\",\n      \"method\": \"Eukaryotic expression system, PCC enzyme activity assay, Western blot for protein levels\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct enzyme activity reconstitution assay with protein stability readout, but single lab, two novel variants only\",\n      \"pmids\": [\"37839763\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PCCB encodes the beta subunit of mitochondrial propionyl-CoA carboxylase (PCC), a dodecameric biotin-dependent enzyme that carboxylates propionyl-CoA to methylmalonyl-CoA; the beta subunit assembles with alpha subunits (PCCA) through interactions mediated by its C-terminal domain (required for heteromeric α-β and homomeric β-β assembly) and N-terminal domain (required for proper folding), and loss of PCCB function globally disrupts TCA cycle flux and mitochondrial oxidative phosphorylation, with emerging evidence that PCCB-dependent mitochondrial metabolism also regulates GABAergic neurotransmitter levels, and that PPDPF can block PCCA-PCCB interaction to suppress PCC activity and methionine catabolism.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PCCB encodes the beta subunit of mitochondrial propionyl-CoA carboxylase (PCC), a biotin-dependent enzyme (EC 6.4.1.3) that carboxylates propionyl-CoA to methylmalonyl-CoA and which assembles as a dodecameric heteropolymer of alpha (PCCA) and beta (PCCB) subunits [#0, #2]. Within this assembly, the beta subunit's C-terminal region mediates both alpha-beta heteromeric and beta-beta homomeric contacts, while N-terminal regions are required for proper folding, so that C-terminal mutations directly abolish assembly whereas N-terminal substitutions act as temperature-sensitive folding defects [#3]. The great majority of pathogenic PCCB variants abolish catalytic activity, and a subset additionally destabilizes the beta-PCC protein, providing the molecular basis for propionic acidemia [#4, #8]. Beyond propionyl-CoA accumulation, loss of PCCB function globally impairs mitochondrial oxidative phosphorylation and constrains distal TCA cycle flux [#5], and PCCB-dependent metabolism feeds GABAergic neurotransmission, since PCCB knockdown lowers GABA levels and dysregulates GABAergic synapse networks with consequent neuronal hyperactivity [#6]. PCC activity is further regulated by PPDPF, which binds PCCA and blocks the PCCA-PCCB interaction to suppress PCC-mediated methionine catabolism [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Established the molecular identity of the PCCB gene product, answering what polypeptide PCCB encodes and where it maps in the genome.\",\n      \"evidence\": \"cDNA cloning with peptide sequence matching and somatic cell hybrid chromosomal assignment\",\n      \"pmids\": [\"3460076\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No information on subunit stoichiometry or assembly\", \"Catalytic mechanism not addressed beyond EC assignment\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Defined the full-length beta-PCC precursor sequence and demonstrated that splicing mutations abolish functional enzyme, linking PCCB lesions to propionic acidemia at the mRNA and genomic level.\",\n      \"evidence\": \"Full-length cDNA cloning and sequencing of RT-PCR and genomic DNA products from a PA patient\",\n      \"pmids\": [\"8225321\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single patient splice defect; spectrum of mutation types not surveyed\", \"No structural mapping of the encoded protein\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed that PCC is a dodecameric alpha-beta heteropolymer and that PCCB versus PCCA mutations differ in their effects on subunit stability, establishing distinct subunit interdependencies.\",\n      \"evidence\": \"Western blot, Northern blot, complementation across patient cell lines\",\n      \"pmids\": [\"10502773\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which protein domains mediate assembly not yet mapped\", \"Mechanism of differential subunit stability unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Localized the assembly determinants within the beta subunit, distinguishing C-terminal mutations that directly block assembly from N-terminal mutations acting as folding defects.\",\n      \"evidence\": \"Mammalian two-hybrid assay at two temperatures with site-directed mutants\",\n      \"pmids\": [\"11749052\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic structure of the assembly interface\", \"Two-hybrid readout is indirect for in vivo dodecamer formation\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Distinguished catalytic loss from protein-instability mechanisms across many PCCB variants, refining genotype-to-mechanism interpretation.\",\n      \"evidence\": \"Transient expression of 18 variants in PCCB-deficient fibroblasts with activity and stability readouts\",\n      \"pmids\": [\"12757933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve structural basis of catalytic loss for individual residues\", \"Folding/degradation pathway not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that PCCB loss disrupts mitochondrial energy metabolism broadly, beyond simple propionyl-CoA accumulation, including OXPHOS capacity and distal TCA flux.\",\n      \"evidence\": \"Genetic deletion of C. elegans pccb-1 with polarography, 13C-glucose GC/MS flux analysis, and lifespan assays\",\n      \"pmids\": [\"29159707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ortholog model; human relevance inferred\", \"Mechanism linking propionyl-CoA buildup to TCA inhibition not directly traced\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected PCCB-dependent mitochondrial metabolism to GABAergic neurotransmission and neural network activity, offering a mechanistic basis for neurological phenotypes.\",\n      \"evidence\": \"shRNA knockdown in human forebrain organoids with RNA-seq, metabolomics, mitochondrial assays, and multielectrode array recording\",\n      \"pmids\": [\"37620341\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link is correlative via knockdown rather than reconstitution\", \"Causal step from TCA flux to GABA synthesis not isolated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Validated additional novel PCCB variants as loss-of-function via direct reconstitution, supporting clinical interpretation of compound lesions.\",\n      \"evidence\": \"Eukaryotic expression of p.G246del and p.S322F with PCC activity and Western blot stability readouts\",\n      \"pmids\": [\"37839763\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, only two variants\", \"Structural impact on the enzyme not modeled\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a regulatory mechanism controlling PCC activity, showing PPDPF binds PCCA and blocks PCCA-PCCB interaction to suppress methionine catabolism.\",\n      \"evidence\": \"Mass spectrometry interaction screen and PPDPF knockdown metabolomics in esophageal squamous cell carcinoma cells\",\n      \"pmids\": [\"39694223\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of PCCB displacement inferred, not shown by reconstitution\", \"PPDPF binds PCCA; direct PCCB contact not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The atomic structure of the assembled human PCC dodecamer and the precise residue-level basis by which beta-subunit mutations and PPDPF regulate alpha-beta assembly remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the assembly interface in the corpus\", \"Direct biochemical reconstitution of PPDPF-mediated disassembly absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 4, 8]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 7]}\n    ],\n    \"complexes\": [\"propionyl-CoA carboxylase (PCC)\"],\n    \"partners\": [\"PCCA\", \"PPDPF\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":4,"faith_total":5,"faith_pct":80.0}}