SUCLA2 Gene

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SUCLA2 Gene

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SUCLA2 Gene

Overview

SUCLA2 encodes the beta subunit of ADP-forming succinyl-CoA synthetase (SCS), also known as succinate-CoA ligase ADP-forming [GDP](/proteins/suclg1-protein) form. This mitochondrial enzyme catalyzes a critical step in the [tricarboxylic acid cycle (TCA cycle)](/mechanisms/citric-acid-cycle) and is essential for cellular [ATP](/proteins/atp) production. SUCLA2 forms a heterodimer with the alpha subunit (SUCLG1) to create the ADP-forming SCS isoform, which is predominantly expressed in tissues with high ATP demand, including [brain](/brain-regions/overview), [heart](/organs/heart), and skeletal muscle. [@sucla2022]

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SUCLA2 Gene

Overview

Mermaid diagram (expand to render)

SUCLA2 encodes the beta subunit of ADP-forming succinyl-CoA synthetase (SCS), also known as succinate-CoA ligase ADP-forming [GDP](/proteins/suclg1-protein) form. This mitochondrial enzyme catalyzes a critical step in the [tricarboxylic acid cycle (TCA cycle)](/mechanisms/citric-acid-cycle) and is essential for cellular [ATP](/proteins/atp) production. SUCLA2 forms a heterodimer with the alpha subunit (SUCLG1) to create the ADP-forming SCS isoform, which is predominantly expressed in tissues with high ATP demand, including [brain](/brain-regions/overview), [heart](/organs/heart), and skeletal muscle. [@sucla2022]

Mutations in SUCLA2 cause mitochondrial DNA depletion syndrome (MTDPS), a severe autosomal recessive disorder characterized by profound mitochondrial dysfunction, encephalomyopathy, and early-onset neurodegeneration. The gene is also implicated in Alzheimer's Disease ([AD](/diseases/alzheimer-disease)) and [Parkinson's Disease](/diseases/parkinson-disease) through its role in mitochondrial energy metabolism and nucleotide homeostasis. [@mtdna2023]

Gene Information

| Property | Value |
|----------|-------|
| Gene Symbol | SUCLA2 |
| Full Name | Succinate-CoA Ligase ADP Forming Subunit Beta |
| Aliases | SCS-β, SUCL-BETA, Beta-succinyl CoA synthetase |
| Chromosomal Location | 13q14.2 |
| NCBI Gene ID | [8802](https://www.ncbi.nlm.nih.gov/gene/8802) |
| OMIM | [603921](https://www.omim.org/entry/603921) |
| Ensembl ID | [ENSG00000147576](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000147576) |
| UniProt | [P53999](https://www.uniprot.org/uniprot/P53999) |
| Protein Class | Mitochondrial Matrix Enzyme |
| Associated Diseases | [Alzheimer Disease](/diseases/alzheimer-disease), [Mitochondrial Encephalomyopathy](/diseases/mitochondrial-encephalomyopathy), Cardiomyopathy, Deafness |

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Protein Structure and Function

Subunit Composition

ADP-forming succinyl-CoA synthetase (SCS) is a heterodimeric enzyme:

α Subunit (SUCLG1):

Molecular weight: ~35 kDa
Binds succinyl-CoA
Catalytic site for CoA release
Essential for enzyme stability

β Subunit (SUCLA2):

Molecular weight: ~42 kDa
Binds ADP/ATP
Provides nucleotide specificity (ADP vs GDP)
Forms the nucleotide-binding pocket

The α-β heterodimer is the minimal functional unit. Assembly occurs in the mitochondrial matrix, requiring proper mitochondrial protein import and folding. [@garcia2014]

Catalytic Mechanism

The SCS reaction proceeds through a two-step mechanism:

Step 1: Succinyl-CoA Binding and Thiolysis

Succinyl-CoA binds to the α subunit active site
The thioester bond is cleaved
Succinate is released, leaving CoA bound to the enzyme

Step 2: Nucleotide Addition (Phosphorylation)

ADP (or GDP for the GTP-forming isoform) enters the β subunit pocket
The CoA-thiolate attacks the ADP's terminal phosphate
ATP (or GTP) is synthesized and released

The overall reaction:
Succinyl-CoA + ADP + Pi ↔ Succinate + ATP + CoA

This is one of only two [ATP](/proteins/atp)-producing steps in the [TCA cycle](/mechanisms/citric-acid-cycle), making SCS essential for aerobic energy metabolism. [@elen2013]

Substrate Specificity

The SUCLA2-containing SCS isoform has distinct properties:

| Property | ADP-Forming (SUCLA2) | GDP-Forming (SUCLG2) |
|----------|---------------------|---------------------|
| Nucleotide | ADP/ATP | GDP/GTP |
| Distribution | Predominant in heart, brain | Predominant in liver, kidney |
| Tissue Specificity | High energy demand tissues | Metabolic tissues |
| Pathogenic Variants | More common | Less common |

The relative ratios of ADP-forming to GDP-forming isoforms vary by tissue, reflecting different metabolic requirements. In the [brain](/brain-regions/overview), the ADP-forming isoform predominates, consistent with the high [ATP](/proteins/atp) demands of [neurons](/cell-types/neurons). [@garcia2014]

Structural Features

The SUCLA2 protein contains:

N-terminal Mitochondrial Targeting Sequence (MTS): Cleaved upon mitochondrial import (~30 amino acids)

Nucleotide-Binding Domain (NBD): Rossmann-like fold that binds ADP/ATP

CoA-binding Domain: On the SUCLG1 α subunit

Inter-subunit Interface: Extensive contact between α and β subunits, essential for stability

Crystal structures reveal that the β subunit undergoes conformational changes during the catalytic cycle, alternating between open and closed states for nucleotide binding and release. [@garcia2014]

Role in Mitochondrial Energy Metabolism

TCA Cycle Integration

SUCLA2 is centrally positioned in mitochondrial metabolism:

Entry Point: Succinyl-CoA, the substrate for SCS, is produced from:

α-ketoglutarate via α-ketoglutarate dehydrogenase (KGDH)
Odd-chain fatty acid oxidation
Catabolism of certain amino acids (isoleucine, methionine, valine)

Exit Points: The products of SCS catalysis feed into:

[ATP](/proteins/atp) production via oxidative phosphorylation
Succinate, which continues in the [TCA cycle](/mechanisms/citric-acid-cycle) to fumarate
Nucleotide pools (via adenylate kinase)

Oxidative Phosphorylation Coupling

The [ATP](/proteins/atp) produced by SCS is directly available for:

Immediate energy needs in the mitochondrial matrix
Export to the cytosol via the adenine nucleotide translocator (ANT)
Maintenance of cellular energy homeostasis

In [neurons](/cell-types/neurons), this localized [ATP](/proteins/atp) production is critical for:

Ion gradient maintenance (Na⁺/K⁺ ATPase)
Synaptic vesicle cycling
Dendritic spine function
Action potential propagation

SUCLA2 deficiency leads to impaired mitochondrial respiration and reduced [ATP](/proteins/atp) production, particularly in tissues with high energy demands. [@bindu2018]

Nucleotide Metabolism

Beyond energy production, SCS connects to nucleotide metabolism:

ATP/ADP Pool Maintenance:

SCS contributes to mitochondrial [ATP](/proteins/atp) synthesis
Adenylate kinase equilibrium: 2 ADP ↔ ATP + AMP
Maintains cellular adenine nucleotide ratios

mtDNA Maintenance:

Mitochondrial [DNA](/proteins/dna) replication requires dNTP pools
SUCLA2 mutations cause mtDNA depletion
dNTP levels are reduced in SUCLA2-deficient cells

Deoxyribonucleotide Synthesis:

Mitochondrial dNTP synthesis is interconnected with [ATP](/proteins/atp) metabolism
Reduced [ATP](/proteins/atp) limits ribonucleotide reductase activity
This impairs mtDNA replication and maintenance [@morvan2019]

Disease Associations

Mitochondrial DNA Depletion Syndrome (MTDPS)

Biallelic mutations in SUCLA2 cause mitochondrial DNA depletion syndrome type V (MTDPS V), also known as "mitochondrial encephalomyopathy with methylmalonic aciduria":

Clinical Features:

Early-onset progressive encephalomyopathy
Severe developmental delay
Hypotonia
Epileptic encephalopathy
Sensorineural hearing loss
Cardiomyopathy
Failure to thrive
Early death (often in childhood)

Biochemical Hallmarks:

mtDNA depletion (reduction to 10-30% of normal)
Elevated methylmalonic acid in urine
Reduced complex I and IV activity
Lactic acidosis

Genetics: Autosomal recessive inheritance. Over 30 pathogenic variants identified:

Missense mutations (most common)
Splice site mutations
Nonsense/frameshift mutations
Large deletions

Pathogenesis: SUCLA2 mutations lead to:

Reduced SCS activity

Impaired succinate production

Disrupted TCA cycle function

Reduced mtDNA maintenance

Progressive mtDNA depletion

Secondary respiratory chain deficiency [@rouzier2012]

Alzheimer's Disease

SUCLA2 expression and function are altered in Alzheimer's disease:

Expression Changes: Post-mortem AD brains show:

Reduced SUCLA2 mRNA in [hippocampus](/brain-regions/hippocampus) and [cortex](/brain-regions/cortex)
Decreased protein levels in affected regions
Reduced enzyme activity

Mechanistic Links:

[Amyloid-beta](/proteins/amyloid-beta) toxicity impairs mitochondrial function
[Tau](/proteins/tau) pathology disrupts mitochondrial dynamics
Energy metabolism is among the earliest deficits in AD
SUCLA2 dysfunction contributes to impaired TCA cycle activity

Therapeutic Implications: Enhancing SUCLA2 expression or activity could:

Restore mitochondrial ATP production
Improve neuronal energy status
Protect against amyloid-beta toxicity
Support synaptic function

Parkinson's Disease

SUCLA2 may play protective roles in dopaminergic neurons:

Mitochondrial Protection: In [substantia nigra](/brain-regions/substantia-nigra) [dopaminergic neurons](/cell-types/dopaminergic-neurons):

High energy requirements make these neurons vulnerable
SUCLA2 supports ATP production
Protects against [alpha-synuclein](/proteins/alpha-synuclein)-induced toxicity

Potential Mechanisms:

Enhanced mitochondrial respiration
Improved calcium handling
Reduced oxidative stress
Better protein quality control

Genetic Associations: While SUCLA2 is not a major PD risk gene, variants may modify disease severity or progression in some populations.

Cardiomyopathy

SUCLA2 mutations can cause cardiomyopathy as part of mitochondrial disease:

Hypertrophic cardiomyopathy more common than dilated
Often accompanied by other mtDNA depletion features
May present in infancy or early childhood
Poor prognosis without intervention

Other Conditions

Hearing Loss: Sensorineural deafness is common in SUCLA2 deficiency:

Likely due to mitochondrial dysfunction in hair cells
May be progressive
Often accompanied by other neurological symptoms

Epilepsy: SUCLA2-related encephalopathy includes:

Infantile spasms
Myoclonic seizures
Focal seizures
Refractory epileptic encephalopathy [@wed2019]

Role in Neuronal Function

Energy Demand in Neurons

[Neurons](/cell-types/neurons) have exceptionally high energy requirements:

Resting Potential: The Na⁺/K⁺ ATPase consumes ~70% of neuronal ATP

Ion gradient maintenance is continuous
Cannot be downregulated without loss of function

Synaptic Activity: Neurotransmitter cycling requires:

Vesicle acidification (V-ATPase)
Ion channel operation
Cytoskeletal dynamics
Exocytosis/endocytosis

Signal Transduction: Second messenger synthesis:

cAMP production
Phospholipid metabolism
Protein phosphorylation

SUCLA2 supports these demands through localized [ATP](/proteins/atp) production in the mitochondrial matrix near areas of high consumption. [@bindu2018]

Calcium Handling

Mitochondria buffer intracellular calcium:

Calcium uptake via mitochondrial calcium uniporter (MCU)
Stimulation of TCA cycle enzymes (including SCS)
Enhancement of ATP production

In neurons:

Calcium signaling regulates synaptic plasticity
Mitochondrial calcium affects release probability
Dysregulated calcium contributes to excitotoxicity

SUCLA2 function is calcium-responsive, providing metabolic support for calcium-dependent signaling. [@bindu2018]

Synaptic Function

Synaptic terminals have specialized energy requirements:

Presynaptic Terminals:

Vesicle cycling is ATP-intensive
Mitochondria are enriched at terminals
SUCLA2 supports local ATP production

Postsynaptic Densities:

Dendritic mitochondria support spine function
ATP-dependent actin dynamics
Receptor trafficking

Implications of Dysfunction: SUCLA2 deficiency leads to:

Impaired synaptic vesicle recycling
Reduced synaptic transmission
Spine abnormalities
Synaptic loss

This parallels the synaptic deficits seen in early AD and PD. [@bindu2018]

Therapeutic Approaches

Gene Therapy

AAV-mediated SUCLA2 delivery is being explored:

Target neurons directly
Cross blood-brain barrier with appropriate serotypes
Restore enzyme function
Prevent disease progression

Challenges:

Delivery to all affected tissues (brain, heart, muscle)
Avoiding immune response
Long-term expression

Small Molecule Therapies

CoQ10 and MitoQ: Antioxidants supporting mitochondrial function L-Carnitine: Supports fatty acid oxidation Riboflavin: Supports complex I activity Dichloroacetate: Stimulates PDH activity N-acetylcysteine: Antioxidant support

These provide partial benefit but do not address the root cause.

Nucleotide Supplementation

Since SUCLA2 deficiency affects nucleotide pools:

dNTP supplementation is being explored
Nucleoside analogs that bypass salvage pathways
Precursor supplementation (adenine, ribose)

Dietary Interventions

Ketogenic Diet: May provide alternative energy substrate Calorie Restriction: May improve mitochondrial function Specific Amino Acid Limitation: Reduce succinyl-CoA production from protein

Outcome Measures in Clinical Trials

mtDNA copy number in muscle/blood
Muscle strength and function
Developmental milestones
Seizure frequency
Hearing function
Cardiac function

Animal Models

Mouse Models

Sucla2 Knockout: Homozygous knockout is embryonic lethal

Severe mtDNA depletion
Impaired development

Heterozygous Mice: Show partial deficiency

Reduced enzyme activity
Increased stress sensitivity
Possible behavioral changes

Conditional Knockouts: Brain-specific deletion shows:

Impaired mitochondrial function
Learning and memory deficits
Age-related degeneration

Zebrafish Models

Morpholino knockdown recapitulates human disease
Used for drug screening
Shows mtDNA depletion and neurological deficits

Interacting Proteins

SUCLA2 interacts with several mitochondrial proteins:

Core Complex:

SUCLG1 (α subunit) — direct subunit interaction
SUCLG2 (GDP-forming β subunit) — tissue-specific variant

Metabolic Enzymes:

α-Ketoglutarate dehydrogenase (KGDH) — upstream in TCA cycle
Succinate dehydrogenase (SDH) — downstream in TCA cycle
Citrate synthase (CS) — TCA cycle entry point

Mitochondrial Translation:

Mitochondrial ribosome components
Translation factors
tRNA synthetases

Quality Control:

Mitochondrial chaperones (Hsp60, mtHsp70)
Proteases (ClpP, LonP1)

Expression Pattern

SUCLA2 shows tissue-specific expression:

| Tissue | Expression Level | Significance |
|--------|------------------|---------------|
| [Brain](/brain-regions/overview) | High | Neuronal energy demands |
| Heart | Very High | Continuous contractile function |
| Skeletal Muscle | High | Exercise-induced demands |
| Kidney | Moderate | Metabolic function |
| Liver | Moderate | Metabolic processing |

In the brain:

Highest in [hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex)
Expressed in [neurons](/cell-types/neurons) and [astrocytes](/cell-types/astrocytes)
Lower in [microglia](/cell-types/microglia) and [oligodendrocytes](/cell-types/oligodendrocytes) [@sucla2021]

Biomarkers

For SUCLA2-related disease:

Genetic Testing: Sequencing for pathogenic variants Biochemical Markers:

Methylmalonic acid in urine (elevated)
Lactic acid in blood (elevated)
Urine organic acids (3-methylglutaconic acid)

Functional Assays:

mtDNA copy number (reduced)
Complex I/IV activity (reduced)
SCS enzyme activity (reduced)

Imaging:

MRI shows T2 hyperintensities in basal ganglia
MR spectroscopy shows elevated lactate

References

[Rouzier C et al., SUCLA2 and mitochondrial disease (2012)](https://pubmed.ncbi.nlm.nih.gov/22633723/)

[Elenbaas B et al., Succinyl-CoA synthetase isoforms in energy metabolism (2013)](https://pubmed.ncbi.nlm.nih.gov/23552654/)

[García-Diaz B et al., SCS isoforms in metabolism (2014)](https://pubmed.ncbi.nlm.nih.gov/25449890/)

[Jerman S et al., SUCLA2 deficiency causes mitochondrial encephalomyopathy (2015)](https://pubmed.ncbi.nlm.nih.gov/25787147/)

[Lightowlers RN et al., Mitochondrial translation defects in neurodegeneration (2015)](https://pubmed.ncbi.nlm.nih.gov/25733754/)

[Bindu PS et al., SUCLA2 in neuronal energy metabolism (2018)](https://pubmed.ncbi.nlm.nih.gov/29652168/)

[Carroll J et al., Mitochondrial DNA depletion syndromes (2018)](https://pubmed.ncbi.nlm.nih.gov/29524741/)

[Kornblum C et al., SUCLA2 and hearing loss in mitochondrial disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29772156/)

[Morvan D et al., Nucleotide metabolism and mtDNA maintenance (2019)](https://pubmed.ncbi.nlm.nih.gov/31150823/)

[Wedel J et al., Epilepsy in SUCLA2 deficiency (2019)](https://pubmed.ncbi.nlm.nih.gov/31256789/)

[Schaller A et al., SUCLA2 mutations in上市公司 (2020)](https://pubmed.ncbi.nlm.nih.gov/32040123/)

[Morigaki R et al., SUCLA2 in mitochondrial ATP synthesis (2021)](https://doi.org/10.1016/j.biochim.2021.104489)

[Garcia-Martinez L et al., SUCLA2 mutations and mitochondrial disease (2022)](https://doi.org/10.1007/s12035-021-02567-6)

[Martinez-Reyes I et al., mtDNA depletion syndrome treatment (2023)](https://doi.org/10.1007/s12035-023-03089-2)

[Kelley N et al., Metabolic therapy approaches (2021)](https://doi.org/10.1007/s12035-020-02289-2)

Pathway Diagram

The following diagram shows the key molecular relationships involving SUCLA2 Gene discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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Related Entities

SUCLA2

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slug	genes-sucla2
kg_node_id	SUCLA2
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-77d8137df7ec
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-sucla2'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

65%

Debates

0

Incoming

13

Outgoing

25

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

SUCLA2 Gene

SUCLA2 Gene

Overview

SUCLA2 Gene

Overview

Gene Information

Protein Structure and Function

Subunit Composition

Catalytic Mechanism

Substrate Specificity

Structural Features

Role in Mitochondrial Energy Metabolism

TCA Cycle Integration

Oxidative Phosphorylation Coupling

Nucleotide Metabolism

Disease Associations

Mitochondrial DNA Depletion Syndrome (MTDPS)

Alzheimer's Disease

Parkinson's Disease

Cardiomyopathy

Other Conditions

Role in Neuronal Function

Energy Demand in Neurons

Calcium Handling

Synaptic Function

Therapeutic Approaches

Gene Therapy

Small Molecule Therapies

Nucleotide Supplementation

Dietary Interventions

Outcome Measures in Clinical Trials

Animal Models

Mouse Models

Zebrafish Models

Interacting Proteins

Expression Pattern

Biomarkers

See Also

References

Pathway Diagram

💬 Discussion