SUCLG1

SUCLG1 encodes the alpha subunit of the mitochondrial matrix succinate-CoA ligase (SUCL), a heterodimer that catalyzes the reversible conversion of succinyl-CoA to succinate and thereby contributes to mitochondrial substrate-level phosphorylation (PMID:20693550, PMID:30470562). SUCLG1 is structurally indispensable to the complex: loss of SUCLG1 protein leads to concurrent loss of the partner beta subunits SUCLA2 and SUCLG2, abolished SCS enzyme activity, mtDNA depletion, and respiration defects, all of which are reversed by ectopic wild-type SUCLG1, establishing SUCLG1 as required for SUCL stability and function (PMID:27484306). Pathogenic SUCLG1 mutations cause this loss of SUCL, impairing mitochondrial substrate-level phosphorylation and producing SUCLG2 mislocalization with increased mitochondrial fragmentation (PMID:30470562). Beyond its catalytic role, SUCLG1 governs the succinyl-CoA pool to restrict succinylation of mitochondrial RNA polymerase POLRMT at K622; by keeping POLRMT hyposuccinylated it preserves POLRMT engagement with mtDNA and transcription factors, sustaining mtDNA transcription and mitochondrial biogenesis—a circuit exploited by FLT3-mutant leukemia, which upregulates SUCLG1 to drive mitobiogenesis and disease progression (PMID:38649537). SUCLG1 enzymatic activity is itself subject to acyl-lysine regulation, with hyperbutyrylation at K90 impairing TCA flux and SIRT4 acting as the debutyrylase that restores activity (PMID:41991142). SUCLG1 supports mitochondrial fusion, mitochondrial quality, and aerobic respiration in proliferating tumor cells (PMID:39749698).

1. 2010 Medium

   Established that SUCLG1 is the alpha subunit of mitochondrial succinate-CoA ligase and that the complex is interdependent, since loss of SUCLG1 also eliminates the SUCLA2 beta subunit.

   Evidence Western blot and minigene splice analysis in patient fibroblasts

   PMID:20693550

   Open questions at the time

   • Did not directly measure enzyme activity loss
   • Interdependence with SUCLG2 not yet examined
   • Mechanism of beta-subunit degradation not defined
2. 2016 High

   Demonstrated through genetic rescue that SUCLG1 is necessary for SUCL complex stability, SCS enzyme activity, mtDNA maintenance, and respiration, moving beyond correlation to causation.

   Evidence Western blot, SCS activity assay, mtDNA quantification, respiration assay, and ectopic WT SUCLG1 rescue in patient fibroblasts

   PMID:27484306

   Open questions at the time

   • Mechanism linking SUCL loss to mtDNA depletion not resolved
   • Single patient-derived cell background
   • No structural basis for complex stabilization
3. 2018 Medium

   Connected a specific pathogenic mutation to functional consequences, showing SUCLG1 loss reduces both beta subunits, impairs substrate-level phosphorylation, and disrupts mitochondrial morphology.

   Evidence Immunoblot, confocal imaging, respirometry, and enzyme assays in patient fibroblasts carrying p.Ala209Glu

   PMID:30470562

   Open questions at the time

   • Causal link between SUCL loss and SUCLG2 mislocalization unexplained
   • mtDNA levels and standard complex activities unchanged here, contrasting earlier findings
   • Mechanism of mitochondrial fragmentation not defined
4. 2024 High

   Revealed a non-canonical regulatory role: SUCLG1 controls the succinyl-CoA pool to limit POLRMT K622 succinylation, thereby sustaining mtDNA transcription and mitochondrial biogenesis, a circuit hijacked in FLT3-mutant leukemia.

   Evidence Succinylation site mapping, POLRMT Co-IP with mtDNA and transcription factors, genetic depletion in mouse/humanized leukemia models, and clinical FLT3-mutant sample analysis

   PMID:38649537

   Open questions at the time

   • Whether non-enzymatic succinyl-CoA buffering is the sole mechanism not established
   • Generality beyond leukemia contexts untested
   • Direct enzyme writer for POLRMT succinylation not identified
5. 2025 Medium

   Showed SUCLG1 supports mitochondrial fusion, quality, aerobic respiration, and tumor cell proliferation/migration in plexiform neurofibroma, extending its role into mitochondrial dynamics and cancer cell metabolism.

   Evidence Knockdown/overexpression with Seahorse, immunofluorescence, electron microscopy, flow cytometry, and qPCR in PNF cell lines

   PMID:39749698

   Open questions at the time

   • SLC25A1 regulation is a single indirect observation
   • Mechanism connecting SUCLG1 to fusion machinery unknown
   • Pathway placement limited to one tumor model
6. 2026 Medium

   Identified acyl-lysine control of SUCLG1 enzymatic activity, with K90 hyperbutyrylation impairing TCA flux and SIRT4 acting as the debutyrylase that restores it, linking metabolic signaling to SUCLG1 function in heart failure.

   Evidence Butyrylome proteomics, SIRT4 inhibitor/overexpression, succinate/ATP measurement in HFpEF mouse and cellular models

   PMID:41991142

   Open questions at the time

   • Direct demonstration that K90 butyrylation alters catalysis at the structural level absent
   • Butyryl-CoA source and writer enzyme not identified
   • Generality beyond HFpEF context untested

• How SUCLG1's catalytic and succinyl-CoA-buffering activities are integrated across tissues, and the structural basis for both complex stabilization and PTM-dependent regulation, remain open.
• No structural model integrating heterodimer assembly with K90/K622 PTM regulation
• Mechanism by which SUCL loss causes mtDNA depletion versus normal mtDNA in different studies unreconciled
• Writer enzymes for SUCLG1 and POLRMT acylation unidentified