Affinage

SEPHS2

Selenide, water dikinase 2 · UniProt Q99611

Length
448 aa
Mass
47.3 kDa
Annotated
2026-06-10
11 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SEPHS2 is a selenophosphate synthetase that supplies the activated selenium donor for selenocysteine biosynthesis, coupling selenium assimilation to selenoprotein production and redox homeostasis (PMID:9012797, PMID:40750759). The enzyme catalyzes selenide-dependent synthesis of selenophosphate from ATP through a catalytically essential active-site selenocysteine, which can be substituted by cysteine but not by alanine, serine, or threonine without loss of activity, establishing a strict requirement for a thiol/selenol nucleophile (PMID:9012797, PMID:10515607). Functionally, SEPHS2 specifically serves a selenite-assimilation route, distinguishing it from its paralog SEPHS1, which operates through a selenocysteine-recycling pathway (PMID:15534230). Within cells SEPHS2 physically associates with the selenocysteine biosynthesis machinery, interacting with SEPSECS and SEPHS1 and forming higher-order oligomers with these factors and SECp43 (PMID:28414460). Its output is gated at the translational level: METTL5-dependent 18S rRNA m6A methylation promotes SEPHS2 translation, and loss of this input lowers SEPHS2 protein, reduces selenoprotein synthesis, raises ROS, and triggers apoptosis (PMID:40750759). Independently of selenoprotein biosynthesis, SEPHS2 also constrains a metabolic axis in which its loss elevates intracellular NAD+, activating SIRT2 to deacetylate and stabilize the gluconeogenic enzyme PCK1, thereby suppressing oxidative phosphorylation and redirecting glucose flux toward gluconeogenesis and the pentose phosphate pathway with consequences for metastasis and PPP-inhibitor sensitivity (PMID:42035418).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 1997 High

    Established that SEPHS2 is a selenophosphate synthetase and that its active-site residue is catalytically essential, defining the enzyme's core chemistry.

    Evidence Baculovirus expression and purification of the Sec→Cys mutant with an in vitro selenide-dependent AMP-formation assay

    PMID:9012797

    Open questions at the time
    • Activity measured on the Sec→Cys mutant rather than the native selenocysteine enzyme
    • No structural model of the active site
  2. 1999 High

    Defined kinetic parameters and the strict chemical requirement at the active site by showing only thiol/hydroxyl-bearing residues support catalysis.

    Evidence E. coli selD complementation plus in vitro kinetics and Cys→Ala/Ser/Thr substitution mutants

    PMID:10515607

    Open questions at the time
    • Complementation uses a bacterial surrogate system
    • Does not address regulation in mammalian cells
  3. 2004 Medium

    Resolved how SEPHS2 differs functionally from its paralog SEPHS1 by showing SEPHS2 supports a selenite-assimilation pathway.

    Evidence Differential E. coli selD complementation with selenite versus L-selenocysteine as selenium source

    PMID:15534230

    Open questions at the time
    • Functional readout was indirect (formate dehydrogenase H activity)
    • Used Sec→Cys mutant for expression
  4. 2017 Medium

    Placed SEPHS2 within a physical selenocysteine biosynthesis complex, connecting its enzymatic output to downstream Sec synthesis machinery.

    Evidence BRET in mammalian cells with co-immunoprecipitation confirmation of SEPHS2–SEPSECS and SEPHS2–SEPHS1 interactions

    PMID:28414460

    Open questions at the time
    • Interaction stoichiometry and complex architecture undefined
    • Single-lab interaction data
  5. 2025 Medium

    Identified a translational control input by showing METTL5-driven rRNA methylation promotes SEPHS2 production, linking ribosome modification to selenoprotein synthesis and ROS control.

    Evidence METTL5 knockdown/knockout with polysome profiling, ROS/apoptosis assays, and SEPHS2 rescue in myeloma cells and xenografts

    PMID:40750759

    Open questions at the time
    • Whether SEPHS2 is a direct versus indirect translational target not fully resolved
    • Generality beyond multiple myeloma untested
  6. 2026 Medium

    Uncovered a selenoprotein-independent role for SEPHS2 in metabolic control via an NAD+–SIRT2–PCK1 axis governing OXPHOS and glucose routing.

    Evidence OXPHOS screen, SEPHS2 KO lines, metabolic flux, NAD+ measurement, SIRT2 activity and PCK1 acetylation/stability assays, plus xenograft metastasis and PPP-inhibitor treatment

    PMID:42035418

    Open questions at the time
    • Mechanism linking SEPHS2 loss to NAD+ elevation not defined
    • Not independently replicated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the catalytic selenophosphate-synthetase function mechanistically connects to the selenoprotein-independent NAD+/metabolic role remains unresolved.
  • No structural mechanism bridging enzymatic and metabolic functions
  • The molecular event by which SEPHS2 sets NAD+ levels is unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 2 GO:0140657 ATP-dependent activity 2 GO:0016874 ligase activity 1
Pathway
R-HSA-392499 Metabolism of proteins 2 R-HSA-1430728 Metabolism 1
Partners
SECP43SEPHS1SEPSECS
Complex memberships
selenocysteine biosynthesis complex

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Mouse fetal SPS2 (SEPHS2) encodes a selenophosphate synthetase; the cysteine-substituted mutant (Sec→Cys) retains selenophosphate synthetase activity as measured by selenide-dependent AMP formation from ATP, demonstrating that the active-site selenocysteine/cysteine is catalytically essential. Baculovirus-insect cell overexpression, purification of Sec→Cys mutant protein, in vitro enzymatic assay (AMP formation from ATP) Proceedings of the National Academy of Sciences of the United States of America High 9012797
1999 Mouse SPS2 (SEPHS2) catalyzes selenophosphate synthesis; the Cys-substituted form complements the E. coli selD mutant and has measurable kinetic parameters (Km for ATP = 0.75 mM, Vmax = 9.23 nmol/min/mg). Substitution of Cys with Ala, Ser, or Thr abolishes complementation activity, establishing that a hydroxyl- or thiol-bearing residue at the active site is strictly required. In vivo complementation assay (E. coli selD mutant), purification of SPS2-CYS, in vitro enzymatic activity measurement, site-directed mutagenesis Molecules and cells High 10515607
2004 Human SPS2 (SEPHS2) specifically functions in a selenite assimilation pathway, whereas paralog SPS1 depends on a selenocysteine-recycling (lyase) pathway; this substrate-specificity difference was established by differential complementation of an E. coli selD mutant with selenite vs. L-selenocysteine as selenium source. In vivo complementation assay in E. coli selD mutant with selenite or L-selenocysteine media; cloning from human lung adenocarcinoma cDNA library; TGA→TGT (Sec→Cys) mutation to allow expression Proceedings of the National Academy of Sciences of the United States of America Medium 15534230
2017 Human SEPHS2 physically interacts with selenocysteine synthase SEPSECS and with paralog SEPHS1 within the selenocysteine biosynthesis machinery in mammalian cells; SEPHS2, SEPHS1, SEPSECS, and SECp43 also form homo- and hetero-oligomers. Bioluminescence resonance energy transfer (BRET) assay in mammalian cells; co-immunoprecipitation confirmation of SEPHS2–SEPSECS and SEPHS2–SEPHS1 interactions Biochemistry Medium 28414460
2025 METTL5-mediated 18S rRNA m6A methylation promotes SEPHS2 translation efficiency; depletion of METTL5 reduces SEPHS2 protein levels, decreases selenoprotein synthesis, elevates ROS, and induces apoptosis in multiple myeloma cells, placing SEPHS2 downstream of METTL5 in a translation-selenoprotein-ROS axis. METTL5 knockdown/knockout in MM cell lines and orthotopic xenograft model; polysome profiling/translation efficiency measurement; ROS assay; apoptosis assay; SEPHS2 rescue experiments Cell death & disease Medium 40750759
2026 SEPHS2 loss suppresses oxidative phosphorylation (OXPHOS) and redirects glucose metabolism toward gluconeogenesis and the pentose phosphate pathway (PPP) via a selenoprotein biosynthesis-independent mechanism: SEPHS2 knockout elevates intracellular NAD+ levels, activating deacetylase SIRT2, which promotes deacetylation-dependent stabilization of the gluconeogenic enzyme PCK1. SEPHS2 loss also promotes lung metastasis and sensitizes tumors to the PPP inhibitor 6-aminonicotinamide. OXPHOS-focused genetic screen; SEPHS2 KO cell lines; metabolic flux analysis; NAD+/NADH measurement; SIRT2 activity assay; PCK1 acetylation/stability assay; in vivo xenograft metastasis model; pharmacological inhibitor treatment Cell reports Medium 42035418
2024 SEPHS2 was identified as a direct binding partner (target protein) of the kinase inhibitor dasatinib in live cells, discovered using the POST-IT proximity-tagging technology. POST-IT (Pup-On-target for Small molecule Target Identification Technology) non-diffusive proximity tagging in live cells; validated in live zebrafish embryos bioRxivpreprint Low bio_10.1101_2024.09.06.611731

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 Selenophosphate synthetase genes from lung adenocarcinoma cells: Sps1 for recycling L-selenocysteine and Sps2 for selenite assimilation. Proceedings of the National Academy of Sciences of the United States of America 63 15534230
1997 Fetal mouse selenophosphate synthetase 2 (SPS2): characterization of the cysteine mutant form overproduced in a baculovirus-insect cell system. Proceedings of the National Academy of Sciences of the United States of America 47 9012797
2019 Structural analysis of human SEPHS2 protein, a selenocysteine machinery component, over-expressed in triple negative breast cancer. Scientific reports 26 31695102
2024 Se Alleviated Pb-Caused Neurotoxicity in Chickens: SPS2-GPx1-GSH-IL-2/IL-17-NO Pathway, Selenoprotein Suppression, Oxidative Stress, and Inflammatory Injury. Antioxidants (Basel, Switzerland) 22 38539903
1987 Increased copy number of the 5' end of the SPS2 gene inhibits sporulation of Saccharomyces cerevisiae. Molecular and cellular biology 21 3302678
2017 Analysis of Novel Interactions between Components of the Selenocysteine Biosynthesis Pathway, SEPHS1, SEPHS2, SEPSECS, and SECp43. Biochemistry 18 28414460
2022 Whole-Genome Sequence Analysis of an Endophytic Fungus Alternaria sp. SPS-2 and Its Biosynthetic Potential of Bioactive Secondary Metabolites. Microorganisms 11 36144391
1999 Fetal mouse selenophosphate synthetase 2 (SPS2): biological activities of mutant forms in Escherichia coli. Molecules and cells 8 10515607
2025 METTL5 regulates SEPHS2-mediated selenoprotein synthesis to promote multiple myeloma survival and progression. Cell death & disease 5 40750759
2026 Evaluating SEPHS2 expression and glutathione peroxidase as biomarkers in recurrent pregnancy loss: a new insight. Biomarkers : biochemical indicators of exposure, response, and susceptibility to chemicals 0 41988776
2026 SEPHS2 loss reprograms cancer metabolism from oxidative phosphorylation to gluconeogenesis via PCK1 stabilization. Cell reports 0 42035418

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