LIAS

LIAS (lipoyl synthase) is a mitochondrial radical SAM enzyme that catalyzes the terminal step of lipoic acid biosynthesis, inserting sulfur atoms into the octanoyl moiety attached to mitochondrial multienzyme complexes including pyruvate dehydrogenase and the glycine cleavage system. The enzyme harbors two [4Fe-4S] clusters—an auxiliary cluster that donates sulfur and a reducing cluster required for SAM cleavage—whose sequential assembly depends on the iron–sulfur cluster donors ISCA2 and ISCU (PMID:33562493). FDX1 directly binds LIAS and promotes its functional interaction with the lipoyl carrier protein GCSH, coupling electron transfer to the lipoylation reaction (PMID:37453661). Loss-of-function mutations in LIAS abolish protein lipoylation, impair mitochondrial energy metabolism, and cause nonketotic hyperglycinemia, as demonstrated by patient studies and rescue with wild-type LIAS (PMID:24334290).

1. 2013 High

   Establishing that LIAS is essential for human mitochondrial protein lipoylation resolved whether lipoic acid in mammals is exclusively diet-derived or also synthesized endogenously, and linked LIAS deficiency to a defined Mendelian disease (nonketotic hyperglycinemia).

   Evidence Patient mutation identification with biochemical assays for lipoylation and pyruvate dehydrogenase/glycine cleavage activity, plus wild-type LIAS transfection rescue in patient cells

   PMID:24334290

   Open questions at the time

   • Catalytic mechanism of human LIAS and identity of its iron–sulfur cluster donors were not yet determined
   • Whether LIAS dysfunction contributes to non-Mendelian disease contexts was unknown
2. 2021 High

   In vitro reconstitution of human LIAS catalysis revealed it is a radical SAM enzyme requiring two [4Fe-4S] clusters assembled sequentially by ISCA2 (auxiliary cluster first) and ISCU (reducing cluster), defining the minimal cofactor requirements for catalytic turnover.

   Evidence Purified recombinant LIAS reconstituted with cluster donor proteins, activity monitored by LC-MS, cluster assembly tracked by EPR spectroscopy, mutagenesis of individual cluster-binding cysteines

   PMID:33562493

   Open questions at the time

   • The electron donor coupling SAM cleavage to sulfur insertion in vivo was not identified
   • No structural model of human LIAS with both clusters bound
3. 2021 Medium

   Demonstrating that Lias overexpression in a diabetic mouse model increases lipoic acid synthase activity, reduces oxidative stress, and attenuates hepatic steatosis established an in vivo link between LIAS-mediated lipoylation and mitochondrial protection beyond rare genetic disease.

   Evidence Transgenic Lias-overexpressing Leprdb/db mice assessed by histopathology, mitochondrial function assays, and oxidative stress markers

   PMID:33263565

   Open questions at the time

   • Mechanism by which increased lipoylation reduces hepatic lipid accumulation was not dissected
   • Findings from a single laboratory and model system
4. 2023 High

   Identification of FDX1 as a direct binding partner of LIAS that promotes the LIAS–GCSH interaction resolved how electron transfer is coupled to the lipoylation reaction and distinguished FDX1's role from its broader function in iron–sulfur cluster biogenesis.

   Evidence Co-immunoprecipitation of endogenous FDX1–LIAS complex, metabolite and transcriptional profiling, loss-of-function studies in mammalian cells

   PMID:36778498 PMID:37453661

   Open questions at the time

   • Stoichiometry and structural basis of the FDX1–LIAS–GCSH ternary complex are unresolved
   • Whether other ferredoxins can substitute for FDX1 in vivo is untested
5. 2023 Medium

   A yeast complementation system (lip5Δ) validated pathogenicity of novel LIAS missense variants, providing a scalable functional assay for clinical variant interpretation.

   Evidence Saccharomyces cerevisiae lip5Δ strain complemented with human LIAS wild-type and mutant alleles, growth rescue on oxidative medium

   PMID:36680912

   Open questions at the time

   • Yeast assay may not capture all human-specific regulatory aspects of LIAS
   • Only a small number of variants tested so far
6. 2025 Medium

   Demonstrating that iron overload disrupts [4Fe-4S] cluster integrity in LIAS, causing defective lipoylation and cuproptosis during ischemia-reperfusion, connected LIAS enzymology to a regulated cell death pathway and identified cluster integrity as a vulnerability node.

   Evidence Hypoxia-reoxygenation cell model with iron chelation and [4Fe-4S] cluster assembly protein overexpression rescuing lipoylation; mouse renal I/R model

   PMID:40753758

   Open questions at the time

   • Single-lab finding; independent replication in other tissue-injury models needed
   • Whether cuproptosis is the dominant death mode downstream of LIAS inactivation vs. bioenergetic failure is unresolved
7. 2025 Medium

   A reported direct PCSK9–LIAS interaction suggested a novel regulatory axis linking lipid metabolism signaling to cuproptosis in cardiomyocytes, but the mechanism by which PCSK9 modulates LIAS activity is unclear.

   Evidence Co-immunoprecipitation and protein docking, mouse cardiac I/R model with PCSK9 inhibitor evolocumab

   PMID:39930254

   Open questions at the time

   • Single Co-IP without reciprocal pull-down or in vitro reconstitution of the direct interaction
   • Functional consequence of PCSK9 binding on LIAS catalytic activity not measured
   • No independent replication

• A structural model of human LIAS in complex with its [4Fe-4S] cluster donors, FDX1, and lipoyl carrier GCSH is lacking, leaving the spatial basis of substrate channeling and sulfur insertion unresolved.
• No crystal or cryo-EM structure of human LIAS
• Kinetic mechanism of dual sulfur insertion from the auxiliary cluster not fully resolved with the human enzyme
• Tissue-specific regulation of LIAS expression and activity is poorly characterized