Affinage

MOCS2

Molybdopterin synthase catalytic subunit · UniProt O96007

Length
188 aa
Mass
20.9 kDa
Annotated
2026-06-10
15 papers in source corpus 6 papers cited in narrative 6 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

MOCS2 catalyzes the second step of the conserved molybdenum cofactor biosynthesis pathway, converting precursor Z to molybdopterin (MPT) as the molybdopterin synthase enzyme (PMID:12754701, PMID:16737835, PMID:40707723). The gene has a bicistronic architecture, encoding two distinct proteins in overlapping reading frames — the small sulfur-carrier subunit MOCS2A and the large catalytic subunit MOCS2B — expressed either from alternatively spliced mRNAs or by independent translation of a bicistronic transcript (PMID:12754701, PMID:16737835). The two subunits assemble into an obligate heterodimeric complex: the C-terminus of MOCS2B mediates binding to both the precursor Z substrate and to MOCS2A, and a mutation eliminating the MOCS2B stop codon abolishes both interactions (PMID:16021469), while MOCS2B protein is degraded in the absence of MOCS2A, establishing co-dependence of the subunits for stability (PMID:16737835). A single nucleotide change disrupting both reading frames reduces MPT synthase complex formation and enzymatic activity, confirming that intact subunit assembly is required for catalysis (PMID:40707723). The conserved sulfur-carrier role of the MOCS2A subunit in endogenous molybdenum cofactor synthesis has been validated genetically in the C. elegans ortholog moc-6 (PMID:35224462).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 2003 High

    Resolved how a single locus produces both subunits of an enzyme, establishing that MOCS2 uses a bicistronic, overlapping reading-frame architecture to encode MOCS2A and MOCS2B as the small and large subunits of molybdopterin synthase.

    Evidence Molecular cloning and alternative splicing/bicistronic mRNA characterization

    PMID:12754701 PMID:16737835

    Open questions at the time
    • Relative stoichiometry and regulation of the two translation products not defined
    • Mechanism of independent translation versus splicing not resolved
  2. 2005 Medium

    Localized the substrate- and partner-binding determinants of the large subunit by showing that the MOCS2B C-terminus is required for binding both precursor Z and MOCS2A.

    Evidence In vitro expression of a stop-codon-loss mutant with precursor Z and MOCS2A binding assays

    PMID:16021469

    Open questions at the time
    • Single lab; no structural model of the binding interface
    • Does not define MOCS2A catalytic contribution
  3. 2006 Medium

    Established subunit co-dependence by demonstrating that MOCS2B protein is degraded without MOCS2A even when both transcripts are produced normally.

    Evidence Western blot of patient fibroblasts with a MOCS2A start-codon deletion plus transcript analysis

    PMID:16737835

    Open questions at the time
    • Degradation pathway for free MOCS2B not identified
    • Single patient-derived material, single lab
  4. 2015 Low

    Linked a specific MOCS2B missense variant (p.S140F) to disrupted protein function, supporting that MOCS2B activity is essential for molybdopterin synthase function.

    Evidence Protein expression studies in patient-derived material and in vitro characterization

    PMID:25709896

    Open questions at the time
    • Limited mechanistic detail reported in abstract
    • Quantitative activity loss not characterized
  5. 2022 Medium

    Provided in vivo genetic confirmation of the MOCS2A sulfur-carrier function by showing the C. elegans ortholog moc-6 is required for endogenous molybdenum cofactor synthesis.

    Evidence CRISPR/Cas9 null allele in C. elegans with biochemical assessment of Moco synthesis

    PMID:35224462

    Open questions at the time
    • Ortholog system; human MOCS2A in vivo requirement inferred
    • Biochemistry of sulfur transfer not directly addressed
  6. 2025 Medium

    Demonstrated that a single variant affecting both overlapping reading frames simultaneously impairs complex assembly and catalysis, directly coupling subunit interaction to enzymatic output.

    Evidence In vitro reconstitution of MPT synthesis activity and complex formation with recombinant proteins

    PMID:40707723

    Open questions at the time
    • Single lab in vitro reconstitution
    • Separate contributions of the two reading-frame changes not deconvolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis of MOCS2A/MOCS2B heterodimer assembly, the sulfur-transfer chemistry of precursor Z conversion in the human enzyme, and the degradation pathway controlling MOCS2B stability remain uncharacterized in the available corpus.
  • No human structural model of the heterodimer
  • Sulfur-transfer mechanism not directly assayed
  • MOCS2B degradation machinery unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 2 GO:0016874 ligase activity 1
Pathway
R-HSA-1430728 Metabolism 3
Partners
MOCS2AMOCS2B
Complex memberships
molybdopterin synthase

Evidence

Reading pass · 6 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 MOCS2 has a bicistronic architecture encoding two proteins (MOCS2A and MOCS2B) in different, overlapping open reading frames. These proteins are expressed either from different mRNAs generated by alternative splicing or by independent translation of a bicistronic mRNA, forming the small and large subunits of molybdopterin synthase respectively. Molecular cloning, alternative splicing analysis, bicistronic mRNA characterization Human mutation High 12754701 16737835
2005 A MOCS2B mutation that eliminates the stop codon (elongating the large subunit) abolishes the binding affinity of MOCS2B for both precursor Z (the substrate) and the small subunit MOCS2A, demonstrating that the C-terminus of MOCS2B is required for substrate binding and subunit interaction. In vitro expression of mutant protein, binding assay for precursor Z and MOCS2A interaction Human genetics Medium 16021469
2006 MOCS2B (large subunit of molybdopterin synthase) is unstable in the absence of MOCS2A (small subunit), revealing that the two subunits are co-dependent for protein stability; both transcripts are produced normally from a deletion removing the MOCS2A start codon, but MOCS2B protein is degraded without its partner. Western blot analysis of patient fibroblasts carrying a deletion removing the MOCS2A start codon; transcript analysis confirming both mRNAs are present Molecular genetics and metabolism Medium 16737835
2022 The C. elegans ortholog of MOCS2A (K10D2.7/moc-6) is necessary for endogenous molybdenum cofactor synthesis, genetically demonstrating the conserved sulfur-carrier function of the MOCS2A subunit in vivo. CRISPR/Cas9 null allele generation in C. elegans; biochemical assessment of Moco synthesis in null mutants microPublication biology Medium 35224462
2025 A variant affecting both overlapping reading frames of MOCS2 (p.Ile82Phe in MOCS2A / p.Leu19Phe in MOCS2B) significantly decreases molybdopterin (MPT) synthase complex formation and MPT synthesis activity in vitro, confirming that both subunit interactions and enzymatic activity are disrupted by this single nucleotide change. In vitro functional characterization of MPT synthesis activity and protein complex formation using recombinant proteins European journal of pediatrics Medium 40707723
2015 The MOCS2B missense mutation p.S140F is pathogenic, as demonstrated by protein expression studies confirming disrupted protein function, placing MOCS2B activity as essential for molybdopterin synthase function. Protein expression studies in patient-derived material and in vitro characterization of the p.S140F variant Meta gene Low 25709896

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 Molybdenum cofactor deficiency: Mutations in GPHN, MOCS1, and MOCS2. Human mutation 106 21031595
2003 Mutations in the molybdenum cofactor biosynthetic genes MOCS1, MOCS2, and GEPH. Human mutation 99 12754701
2005 Ten novel mutations in the molybdenum cofactor genes MOCS1 and MOCS2 and in vitro characterization of a MOCS2 mutation that abolishes the binding ability of molybdopterin synthase. Human genetics 22 16021469
2019 The Clinical and Molecular Characteristics of Molybdenum Cofactor Deficiency Due to MOCS2 Mutations. Pediatric neurology 16 31201073
2006 A novel MOCS2 mutation reveals coordinated expression of the small and large subunit of molybdopterin synthase. Molecular genetics and metabolism 16 16737835
2015 Investigation of molybdenum cofactor deficiency due to MOCS2 deficiency in a newborn baby. Meta gene 14 25709896
2022 moc-6/MOCS2A is necessary for molybdenum cofactor synthesis in C. elegans. microPublication biology 7 35224462
2022 Beyond Moco Biosynthesis-Moonlighting Roles of MoaE and MOCS2. Molecules (Basel, Switzerland) 3 35744859
2021 Genotype-Phenotype Dissociation in Two Taiwanese Children with Molybdenum Cofactor Deficiency Caused by MOCS2 Mutation. Neuropediatrics 3 34674206
2020 Proteins Structure Models in the Evaluation of Novel Variant (C.472_477del) in the MOCS2 Gene. Diagnostics (Basel, Switzerland) 3 33066491
2025 A prevalent MOCS2 variant in the Roma population is associated with a novel mild form of molybdenum cofactor deficiency. European journal of pediatrics 2 40707723
2024 Exome Sequencing of Consanguineous Pashtun Families With Familial Epilepsy Reveals Causative and Candidate Variants in TSEN54, MOCS2, and OPHN1. Clinical genetics 1 39400946
2023 Live Birth of a Healthy Child in a Couple with Identical mtDNA Carrying a Pathogenic c.471_477delTTTAAAAinsG Variant in the MOCS2 Gene. Genes 1 36980992
2026 Two mild phenotype molybdenum cofactor deficiency patients with novel MOCS2 mutation and immunological treatment after COVID-19 infection. BMC neurology 0 41731370
2024 A case report of MoCD etiology in a neonate: A novel homozygous MoCS2 variant. Clinical case reports 0 39005576

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