Affinage

NHLRC1

E3 ubiquitin-protein ligase NHLRC1 · UniProt Q6VVB1

Length
395 aa
Mass
42.3 kDa
Annotated
2026-06-10
28 papers in source corpus 9 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/6 claims corpus-supported (83%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NHLRC1 encodes malin, a RING finger E3 ubiquitin ligase that operates with the laforin phosphatase at the endoplasmic reticulum to safeguard glycogen integrity, and whose loss causes the progressive myoclonic epilepsy of Lafora disease (PMID:12958597, PMID:19267391). Malin and laforin colocalize at the ER and function as a complex regulating glycogen metabolism, such that loss of either protein leads to accumulation of insoluble polyglucosan (Lafora bodies) (PMID:12958597, PMID:19267391). Mechanistically, malin's ubiquitin ligase activity degrades laforin itself and the glycogen-synthesis regulator R5/PTG, and disease-associated missense mutations abolish this turnover: the H187P mutation impairs laforin degradation (PMID:19322595), while C46Y, P69A, D146N, and L261P fail to downregulate R5/PTG and cause abnormal intracellular glycogen accumulation (PMID:21505799). Other Lafora-causing mutations instead mislocalize malin to the nucleus or perinuclear aggregates, providing a second route to loss of function (PMID:18311786). Malin loss-of-function is directly causative: AAV-mediated EPM2B restoration in Epm2b-/- mice reverses neuropathology, restores neuronal excitability and synaptic plasticity, and prevents Lafora body formation (PMID:41169091). Beyond this glycogen-protective role, knockdown studies report malin as an activator of AKT signaling in a lung cancer context (PMID:36142605), though this lies outside the characterized neuronal pathway.

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2003 Medium

    Established the molecular identity of malin and placed it in a shared pathway with laforin, answering what the second Lafora disease gene encodes and where it acts.

    Evidence Positional cloning of NHLRC1/EPM2B identifying a RING finger + six NHL motif protein; ER colocalization with laforin by cell imaging

    PMID:12958597 PMID:19267391

    Open questions at the time
    • E3 ligase activity inferred from domains, not reconstituted
    • physical interaction with laforin shown by colocalization rather than direct biochemistry
    • no substrate identified at this stage
  2. 2008 Medium

    Showed that some disease mutations act by mislocalizing malin away from its normal compartment, defining altered subcellular localization as one molecular basis of Lafora disease.

    Evidence Expression of six NHLRC1 missense mutants in cultured cells with localization analysis (nuclear targeting, perinuclear aggregation)

    PMID:18311786

    Open questions at the time
    • no functional rescue linking mislocalization to loss of ligase activity
    • single lab
    • two of six mutants showed no localization change, leaving their mechanism unexplained
  3. 2009 Medium

    Provided direct functional evidence that malin acts as an E3 ligase toward laforin, converting the domain-based prediction into a demonstrated enzyme-substrate relationship.

    Evidence In vitro degradation assay showing H187P mutant fails to degrade laforin in cultured mammalian cells

    PMID:19322595

    Open questions at the time
    • single mutant tested
    • ubiquitination per se not directly visualized
    • single lab
  4. 2011 Medium

    Identified R5/PTG as a second malin target and connected malin's ligase activity to glycogen metabolism, explaining how its loss produces glycogen overaccumulation.

    Evidence Expression of four NHLRC1 mutants in cells with R5/PTG protein levels and intracellular glycogen as orthogonal readouts

    PMID:21505799

    Open questions at the time
    • direct ubiquitination of R5/PTG not shown in this assay
    • single lab
    • relative contribution of R5/PTG vs laforin turnover to disease unresolved
  5. 2018 Low

    Linked malin dysfunction to failure of protein-quality-control clearance, showing that resulting aggregates engage both ubiquitin-proteasome and autophagy machinery.

    Evidence Immunohistochemistry of canine Lafora disease brain polyglucosan bodies positive for ubiquitin, LC3, p62, laforin, and chaperones

    PMID:29444631

    Open questions at the time
    • descriptive marker colocalization without functional manipulation
    • causality between malin loss and clearance failure inferred, not tested
    • animal-tissue observation only
  6. 2022 Low

    Raised a non-neuronal role for malin as an AKT pathway activator, extending its proposed functions beyond glycogen regulation.

    Evidence siRNA knockdown of NHLRC1 in lung cancer lines with pS473-AKT Western blot and proliferation/migration/invasion assays

    PMID:36142605

    Open questions at the time
    • no rescue or mechanistic link to ligase activity
    • cancer context distinct from canonical neuronal function
    • single knockdown approach, single lab
  7. 2024 Low

    Connected malin loss to glial inflammation and neurotransmitter-receptor dysregulation, addressing how glycogen pathology translates into neuronal hyperexcitability.

    Evidence Western blot and immunofluorescence in Epm2b-/- mouse hippocampus implicating glutamatergic/GABAergic subunit changes in glia via TNF/IL-6 signaling (preprint)

    Open questions at the time
    • preprint, not peer-reviewed
    • descriptive measurements without functional rescue
    • causal direction between inflammation and receptor changes untested
  8. 2025 Medium

    Demonstrated that malin loss is the direct, sufficient cause of Lafora phenotypes and that gene restoration reverses them, establishing causality and therapeutic tractability.

    Evidence Intravenous rAAV2/9P31-EPM2B delivery in Epm2b-/- mice with histopathology, electrophysiology, and behavioral readouts

    PMID:41169091

    Open questions at the time
    • single lab
    • durability and dosing window not defined
    • molecular requirement for ligase activity in the rescue not dissected
  9. 2026 Medium

    Revealed an asymmetry in overexpression safety between laforin and malin, informing gene-therapy design by showing only laforin excess is toxic and that toxicity is enzyme-independent.

    Evidence Intrathecal AAV9 overexpression of EPM2A vs EPM2B with enzymatic-activity mutants in mice; histopathology and neurophysiology

    PMID:41825228

    Open questions at the time
    • mechanism of enzyme-independent laforin toxicity unresolved
    • single lab
    • DRG-preferential effect not mechanistically explained

Open questions

Synthesis pass · forward-looking unresolved questions
  • Whether the malin-laforin complex assembly, the direct ubiquitination chemistry, and the full substrate repertoire can be reconstituted biochemically remains unresolved.
  • no in vitro reconstitution of malin ligase activity in the corpus
  • direct ubiquitin transfer to laforin/R5-PTG not visualized
  • structural basis of malin-laforin interaction uncharacterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016740 transferase activity 3 GO:0140096 catalytic activity, acting on a protein 2
Localization
GO:0005783 endoplasmic reticulum 1
Pathway
GO:0140096 catalytic activity, acting on a protein 1
Partners
EPM2APPP1R3C
Complex memberships
laforin-malin complex

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 NHLRC1 (EPM2B) encodes malin, a protein containing a RING finger domain and six NHL motifs, consistent with a putative E3 ubiquitin ligase. Malin and laforin (EPM2A) colocalize to the endoplasmic reticulum, suggesting they operate in a related pathway protecting against polyglucosan accumulation. Gene identification by positional cloning; colocalization by cell imaging Nature genetics Medium 12958597
2008 NHLRC1 disease-associated missense mutations alter the subcellular localization of malin: three mutants (of six tested) targeted the nucleus, one formed perinuclear aggregates, and two showed no significant difference compared to wild-type malin, suggesting that altered subcellular localization of mutant malin is a molecular basis of Lafora disease. Expression of NHLRC1 missense mutants in cultured cells with subcellular localization analysis Human mutation Medium 18311786
2009 The NHLRC1 missense mutation H187P impairs malin's ability to degrade laforin in vitro, directly linking this mutation to loss of malin E3 ubiquitin ligase function toward its substrate laforin. In vitro degradation assay of laforin by mutant malin (H187P) in cultured mammalian cells Neurogenetics Medium 19322595
2011 Disease-associated NHLRC1 mutations (C46Y, P69A, D146N, L261P) cause failure to downregulate R5/PTG (a regulatory subunit of protein phosphatase 1 involved in glycogen synthesis) and lead to abnormal intracellular glycogen accumulation in cultured mammalian cells, demonstrating that malin regulates glycogen metabolism through control of R5/PTG levels. Expression of NHLRC1 mutants in cultured mammalian cells; measurement of R5/PTG protein levels and intracellular glycogen accumulation Journal of molecular medicine (Berlin, Germany) Medium 21505799
2003 Laforin and malin interact with each other and function as a complex that regulates glycogen metabolism; loss of either protein leads to polyglucosan (Lafora body) accumulation. Genetic and cell biological evidence from patient mutations and colocalization studies; complex function inferred from genetic epistasis Human mutation Medium 12958597 19267391
2022 NHLRC1 knockdown in lung cancer cells reduced AKT phosphorylation at serine 473, attenuated cell proliferation, viability, migration, and invasion, and caused expression of pro-apoptotic AKT-repressed genes, identifying malin as a novel AKT activator in a cancer cell context. siRNA knockdown of NHLRC1 in lung cancer cell lines; measurement of AKT phosphorylation (pS473) by Western blot; cell proliferation, viability, migration, and invasion assays International journal of molecular sciences Low 36142605
2018 In canine Lafora disease caused by EPM2B repeat expansion, polyglucosan bodies accumulate in neurons and are positive for laforin, hsp70, α/β-synuclein, ubiquitin, LC3, and p62, demonstrating that malin dysfunction leads to failure of ubiquitin-proteasome and autophagy pathway clearance of abnormal glycogen aggregates. Immunohistochemistry of polyglucosan bodies in canine Lafora disease brain tissue with markers for laforin, ubiquitin, autophagy receptors (LC3, p62), and chaperones Veterinary pathology Low 29444631
2025 Intravenous delivery of rAAV2/9P31 carrying the EPM2B gene reversed neuropathological features, restored neuronal excitability and synaptic plasticity, and prevented Lafora body formation in Epm2b-/- mice, confirming that malin loss of function is the direct cause of these disease phenotypes and that EPM2B gene restoration is sufficient to rescue them. AAV-mediated gene delivery in Epm2b-/- mouse model; histopathology, electrophysiology, and behavioral assays Clinical and translational medicine Medium 41169091
2026 Overexpression of laforin (EPM2A) — but not malin (EPM2B) — paradoxically causes Lafora body formation independently of laforin and malin's enzymatic activities, and this occurs preferentially in dorsal root ganglia; in contrast, malin overexpression does not produce this toxic effect, indicating an asymmetry in the two proteins' safe overexpression profiles relevant to gene therapy. Intrathecal AAV9-based overexpression of EPM2A and EPM2B in mice; histopathology, neurophysiology; enzymatic activity mutants tested Neurotherapeutics Medium 41825228
2024 In Epm2b-/- mice, loss of malin leads to dysregulation of glutamatergic receptor subunits (phospho-GluN2B, phospho-GluA2, GluK2) and increased GAT1 GABA transporter levels in hippocampus, with these changes occurring in activated microglia and reactive astrocytes rather than neurons, mediated via TNF and IL-6 inflammatory signaling pathways. Western blotting, immunofluorescence in Epm2b-/- mouse hippocampus; pathway analysis of TNF/IL-6 signaling bioRxivpreprint Low

Source papers

Stage 0 corpus · 28 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2003 Mutations in NHLRC1 cause progressive myoclonus epilepsy. Nature genetics 254 12958597
2005 Lafora disease due to EPM2B mutations: a clinical and genetic study. Neurology 85 15781812
2009 Lafora progressive myoclonus epilepsy: a meta-analysis of reported mutations in the first decade following the discovery of the EPM2A and NHLRC1 genes. Human mutation 80 19267391
2003 Genetic mapping of a new Lafora progressive myoclonus epilepsy locus (EPM2B) on 6p22. Journal of medical genetics 59 12960212
2005 Late-onset and slow-progressing Lafora disease in four siblings with EPM2B mutation. Epilepsia 54 16190947
2006 Novel NHLRC1 mutations and genotype-phenotype correlations in patients with Lafora's progressive myoclonic epilepsy. Journal of medical genetics 44 16950819
2005 Lafora progressive Myoclonus Epilepsy mutation database-EPM2A and NHLRC1 (EPM2B) genes. Human mutation 43 16134145
2010 Novel mutations in EPM2A and NHLRC1 widen the spectrum of Lafora disease. Epilepsia 35 20738377
2005 Mutations in the NHLRC1 gene are the common cause for Lafora disease in the Japanese population. Journal of human genetics 28 16021330
2009 Novel mutation in the NHLRC1 gene in a Malian family with a severe phenotype of Lafora disease. Neurogenetics 23 19322595
2016 NHLRC1 repeat expansion in two beagles with Lafora disease. The Journal of small animal practice 22 27747878
2018 Accumulation of Laforin and Other Related Proteins in Canine Lafora Disease With EPM2B Repeat Expansion. Veterinary pathology 18 29444631
2011 Lafora progressive myoclonus epilepsy: NHLRC1 mutations affect glycogen metabolism. Journal of molecular medicine (Berlin, Germany) 18 21505799
2008 Lafora disease in the Indian population: EPM2A and NHLRC1 gene mutations and their impact on subcellular localization of laforin and malin. Human mutation 15 18311786
2017 Severe and rapidly-progressive Lafora disease associated with NHLRC1 mutation: a case report. The International journal of neuroscience 14 28556688
2013 Lafora disease: severe phenotype associated with homozygous deletion of the NHLRC1 gene. Journal of the neurological sciences 11 23317923
2011 Rapidly progressive phenotype of Lafora disease associated with a novel NHLRC1 mutation. Pediatric neurology 10 21555062
2018 A recurrent homozygous NHLRC1 variant in siblings with Lafora disease. Human genome variation 9 30083360
2011 Four novel and two recurrent NHLRC1 (EPM2B) and EPM2A gene mutations leading to Lafora disease in six Turkish families. Epilepsy research 8 22047982
2021 NHLRC1 homozygous dodecamer expansion in a Newfoundland dog with Lafora disease. The Journal of small animal practice 7 34263924
2025 Advances in gene therapy for Lafora disease: Intravenous recombinant adeno-associated virus-mediated delivery of EPM2A and EPM2B genes. Clinical and translational medicine 5 41169091
2022 Identification of NHLRC1 as a Novel AKT Activator from a Lung Cancer Epigenome-Wide Association Study (EWAS). International journal of molecular sciences 3 36142605
2021 The rare rs769301934 variant in NHLRC1 is a common cause of Lafora disease in Turkey. Journal of human genetics 3 34117373
2025 Adeno-Associated Virus-Based Gene Therapy for Lafora Disease in Epm2b-Deficient Mice. International journal of molecular sciences 2 41465357
2022 Compound heterozygosity for novel variations of the NHLRC1 Gene in a family with Lafora disease. Clinical neurology and neurosurgery 2 35569391
2026 Lafora disease gene therapy: EPM2A but not EPM2B overexpression results in Lafora body formation. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 1 41825228
2025 Identification of a pathogenic NHLRC1 variant in a consanguineous Pakistani family affected with severe and rapidly progressive Lafora disease. Acta epileptologica 1 40217338
2026 Epm2bP71A and Epm2bD148N knock-in mouse models of Lafora disease exhibit distinct and pronounced neurological alterations. Progress in neurobiology 0 41936809

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