ADSS2

ADSS2 (non-muscle adenylosuccinate synthetase 2) catalyzes the first committed step of de novo and salvage AMP synthesis, converting IMP and aspartate to adenylosuccinate (S-AMP), an activity demonstrated for the recombinant enzyme and shown to restore purine prototrophy when human chromosome 1 corrects an ADSS-deficient mutant (PMID:2004783, PMID:15786719). Within cells this catalytic step is spatially organized: ADSS associates with the purinosome, a multienzyme assembly whose formation under purine depletion accompanies elevated IMP and increased de novo purine biosynthetic flux (PMID:25605736). The S-AMP it produces functions beyond bulk nucleotide supply as a signaling metabolite — in pancreatic β cells glucose drives ADSS-dependent S-AMP production that amplifies insulin exocytosis in a SENP1-dependent manner, and this same ADSS/S-AMP axis underlies the proliferative and anti-apoptotic actions of the antidiabetic agent imeglimin (PMID:26411681, PMID:40638403). ADSS2 is distinguished from its striated-muscle paralog ADSS1 by broad tissue expression and reciprocal transcriptional regulation: cardiomyocyte electrical pacing represses Adss2 while activating Adss1 through calcineurin/NFAT3/GATA4 (PMID:10636885). ADSS expression is further controlled by transcriptional inputs including PPARγ binding to the Adss promoter, with thiazolidinedione treatment raising ADSS and shifting purine metabolism toward AMP accumulation (PMID:24164426). The enzyme is also a substrate of the CUL3-KCTD13 ubiquitin ligase in neurons, where loss of ubiquitination elevates the downstream metabolite succinyl-adenosine (PMID:33409479). Through its position in the purine nucleotide cycle, ADSS activity influences cellular AMP/ATP balance and AMPK regulation (PMID:24164426, PMID:36058289).

1. 1989 Medium

   Established that adenylosuccinate synthetase is not merely a soluble metabolic enzyme but physically associates with the contractile apparatus, raising the possibility of spatial organization of purine metabolism in muscle.

   Evidence In vitro binding assays of purified muscle AdSS with F-actin, thin filaments, and myofibrils under physiological conditions

   PMID:2750889

   Open questions at the time

   • Concerns the muscle isozyme rather than ADSS2 specifically
   • Functional consequence of thin-filament association not demonstrated
2. 1994 Medium

   Localized the human ADSS gene to chromosome 1 and confirmed that the gene product carries adenylosuccinate synthetase activity by rescuing a purine-auxotrophic mutant.

   Evidence Somatic cell hybridization, segregant analysis, and enzyme activity assays complementing the ADSS-deficient CHO mutant

   PMID:2004783

   Open questions at the time

   • Does not distinguish ADSS2 from the muscle isoform at the activity level
   • No structural detail of the enzyme
3. 2000 High

   Defined the reciprocal transcriptional logic separating the two isozymes, showing that contractile/calcium signaling activates the muscle isoform while repressing the non-muscle ADSS2 isoform.

   Evidence Electrical pacing of cardiomyocytes with NFAT-site mutagenesis, reporter assays, and calcineurin pathway inhibition

   PMID:10636885

   Open questions at the time

   • Mechanism repressing Adss2 (versus activating Adss1) not dissected
   • Direct cis-elements controlling Adss2 not mapped
4. 2005 Medium

   Demonstrated the recombinant enzyme's catalytic activity and cytoplasmic localization, and noted ADSS2's broad, non-muscle-restricted expression pattern.

   Evidence Recombinant enzymatic assay, COS-7 overexpression localization, RT-PCR tissue distribution

   PMID:15786719

   Open questions at the time

   • Most enzymatic characterization is on the muscle isozyme; ADSS2-specific kinetics limited
   • Localization inferred from overexpression
5. 2013 Medium

   Identified a transcriptional input (PPARγ) regulating Adss and linked altered Adss expression to AMP accumulation and AMPK signaling, embedding the enzyme in metabolic stress regulation.

   Evidence ChIP confirming PPARγ binding to the Adss promoter, qRT-PCR, NMR metabolomics, AMPK activation assays in rat cardiac tissue

   PMID:24164426

   Open questions at the time

   • Isoform specificity of the PPARγ-regulated Adss not resolved
   • Causality between ADSS level and AMPK not established by direct ADSS manipulation
6. 2015 High

   Recast ADSS-generated S-AMP as a signaling metabolite rather than a metabolic intermediate, showing it amplifies β-cell insulin exocytosis through SENP1.

   Evidence Metabolomics, pharmacological ADSS inhibition, siRNA, and patch-clamp electrophysiology with direct S-AMP addition to human β cells

   PMID:26411681

   Open questions at the time

   • Molecular target of S-AMP downstream of SENP1 not identified
   • Whether ADSS1 or ADSS2 supplies the relevant S-AMP not resolved
7. 2015 Medium

   Placed ADSS within the purinosome and linked the assembly of this multienzyme body to upregulated de novo purine flux, suggesting spatial channeling of the AMP-branch reaction.

   Evidence Fluorescence microscopy of purinosome assembly, purine nucleotide metabolomics, isotopic flux measurements in HeLa cells

   PMID:25605736

   Open questions at the time

   • ADSS's specific contribution inferred from membership, not direct functional dissection within the complex
   • Binding partners that recruit ADSS unidentified
8. 2020 Medium

   Identified post-translational control of ADSS, establishing it as a CUL3-KCTD13 ubiquitin ligase substrate whose dysregulation alters purine-derived metabolite levels in neurons.

   Evidence Ubiquitylome MS comparison of Kctd13 mutant vs wild-type neurons, S-Ado metabolite quantification, ADSS inhibitor rescue

   PMID:33409479

   Open questions at the time

   • Ubiquitination site and consequence (degradation vs activity) not defined
   • Direct ADSS-KCTD13 binding not reciprocally validated
9. 2022 Low

   Positioned ADSS as a regulatory node in the purine nucleotide cycle controlling AMPK activation in insulin-resistant muscle.

   Evidence Metformin treatment of fructose-fed rats with Western blot/qPCR for ADSS and AMPD1, AMP/ATP ratio and AMPK phosphorylation assays

   PMID:36058289

   Open questions at the time

   • Expression-level correlation without direct ADSS manipulation to establish causality
   • Isoform contributing to the muscle effect not specified
10. 2025 Medium

    Extended the β-cell S-AMP signaling model to drug action, showing ADSS-mediated S-AMP production is the mechanistic basis for imeglimin's proliferative and anti-apoptotic effects.

    Evidence ADSS pharmacological inhibition across mouse, human, porcine islets and stem-cell-derived β cells with proliferation/apoptosis assays and S-AMP quantification

    PMID:40638403

    Open questions at the time

    • Downstream effectors of S-AMP in proliferation/apoptosis not mapped
    • Inhibitor selectivity between ADSS isoforms not addressed
11. 2025 Medium

    Connected loss of AdSS activity to genome instability, showing IMP accumulation upon ortholog deletion drives error-prone DNA polymerase ζ-dependent mutagenesis.

    Evidence GC-MS metabolite profiling, growth/division, and mutagenesis assays in S. cerevisiae ade12 mutants

    PMID:40331943

    Open questions at the time

    • Demonstrated in yeast ortholog; relevance to human ADSS2 not tested
    • Mechanism linking IMP buildup to polymerase ζ recruitment unknown

• It remains unresolved which functions are isoform-specific to ADSS2 versus shared with ADSS1, how S-AMP is sensed downstream, and what governs ADSS2 recruitment to the purinosome.
• No structural model of human ADSS2
• Downstream S-AMP receptor/effector unidentified
• Purinosome recruitment determinants for ADSS2 unknown