SIRT5 - Sirtuin 5

SIRT5 - Sirtuin 5

Overview

SIRT5 - Sirtuin 5

Overview

SIRT5 (Sirtuin 5) is a member of the sirtuin family of NAD+-dependent protein deacylases that is primarily localized to mitochondria. Unlike other sirtuins, SIRT5 possesses unique enzymatic activities including desuccinylation, demalonylation, and deglutarylation, in addition to a weak deacetylase activity [1][2][3]. This enzyme plays critical roles in regulating mitochondrial metabolism, the urea cycle, fatty acid oxidation, and cellular stress responses. Recent research has demonstrated that SIRT5 is dysregulated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and other neurodegenerative conditions, making it an attractive therapeutic target [9][10][12][15].

<div class="infobox infobox-gene">

| | |
|---|---|
| Gene Symbol | SIRT5 |
| Full Name | Sirtuin 5 |
| Chromosome | 6p23 |
| NCBI Gene ID | 83737 |
| OMIM | 604603 |
| Ensembl ID | ENSG00000124587 |
| UniProt ID | Q9NXE1 |
| Protein Family | Sirtuin family (class I) |
| Subcellular Location | Mitochondria (primary), nucleus (minor) |
| Associated Diseases | [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), Cancer, Metabolic disorders |

</div>

Enzyme Structure and Function

Protein Structure

SIRT5 is a 310-amino acid protein with a conserved sirtuin core domain. The structure includes:

• N-terminal region: Contains a mitochondrial targeting sequence (MTS) that directs import into mitochondria
• Core domain: The catalytic Rossmann-fold domain (~275 aa) that mediates NAD⁺ binding and deacylation reactions
• Active site: Contains the signature SIRT5 sequence motif (HYGF) that distinguishes it from other sirtuins

Unique Enzymatic Activities

SIRT5 exhibits three distinct demidase activities that are not found in other sirtuins:

1. Desuccinylation (Primary Activity)

• Removes succinyl groups (COO⁻-CH₂-CH₂-COO⁻) from lysine residues
• Major activity of SIRT5 in mitochondria
• Regulates key metabolic enzymes including SDH, GLUD1, and HMGCS2

• Removes malonyl groups (COO⁻-CH₂-COO⁻) from proteins
• Activity similar to desuccinylation but with smaller substrate
• Involved in regulation of glycolytic enzymes

• Removes glutaryl groups (COO⁻-(CH₂)₃-COO⁻) from proteins
• Largest substrate for SIRT5's demidase activity
• Regulates enzymes in the urea cycle and amino acid metabolism

• SIRT5 has minimal deacetylase activity compared to SIRT1-3
• Some reports suggest activity toward specific substrates under certain conditions

Catalytic Mechanism

The demidase reactions proceed through a two-step mechanism:

This mechanism is distinct from classic deacetylation, which releases acetate. The succinate, malonate, and glutarate products are intermediates in central carbon metabolism.

Mitochondrial Metabolic Regulation

Key Substrates and Functions

SIRT5 regulates several critical mitochondrial enzymes:

| Enzyme | Function | SIRT5 Regulation |
|--------|----------|-----------------|
| GLUD1 | Glutamate dehydrogenase | Desuccinylation activates, regulates ammonia detoxification [17] |
| HMGCS2 | Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 | Desuccinylation promotes ketogenesis |
| SDH | Succinate dehydrogenase | Desuccinylation increases activity, regulates complex II |
| CPS1 | Carbamoyl phosphate synthetase 1 | Desuccinylation activates, first step of urea cycle [18] |
| GAPDH | Glyceraldehyde-3-phosphate dehydrogenase | Demalonylation regulates glycolysis |
| IDH2 | Isocitrate dehydrogenase 2 | Desuccinylation enhances activity |

Metabolic Pathways Affected

Urea Cycle: SIRT5 desuccinylates CPS1, the rate-limiting enzyme of the urea cycle, enhancing ammonia detoxification. Loss of SIRT5 leads to elevated ammonia, particularly in liver [18].

Ketogenesis: SIRT5 regulates HMGCS2, the key enzyme for ketone body synthesis. Desuccinylation activates HMGCS2, promoting ketogenesis during fasting.

Fatty Acid Oxidation: SIRT5 modulates enzymes involved in β-oxidation, affecting cellular energy metabolism.

TCA Cycle: SDH and IDH2 regulation connects SIRT5 to central carbon metabolism and mitochondrial respiration.

Role in Neurodegenerative Diseases

Alzheimer's Disease

SIRT5 is significantly affected in AD pathophysiology [9][12][14][20]:

Mitochondrial Dysfunction

• SIRT5 expression is reduced in AD brain tissue
• Succinylome analysis reveals widespread protein hypersuccinylation in AD models
• Restoration of SIRT5 improves mitochondrial function in cellular models

Amyloid Interaction

• Aβ exposure reduces SIRT5 levels in neurons
• SIRT5 loss exacerbates Aβ-induced mitochondrial dysfunction
• SIRT5 activators may protect against Aβ toxicity

Tau Pathology

• SIRT5 regulates tau acetylation and phosphorylation [12]
• Desuccinylation of tau may affect aggregation properties
• SIRT5 deficiency promotes tau pathology in models

Therapeutic Implications

• SIRT5 activators are being explored as AD therapeutics
• Enhancing SIRT5 activity may restore mitochondrial function
• Protecting against succinylotoxicity in neurons

Parkinson's Disease

SIRT5 plays protective roles in PD models [10][11]:

Mitochondrial Complex I

• SIRT5 maintains complex I activity in dopaminergic neurons
• MPTP-induced toxicity is exacerbated by SIRT5 deficiency
• SIRT5 protects against rotenone-induced mitochondrial dysfunction

Alpha-Synuclein

• SIRT5 regulates autophagy of damaged mitochondria (mitophagy)
• Loss of SIRT5 impairs clearance of α-synuclein aggregates
• SIRT5 activity affects mitochondrial quality control

Oxidative Stress

• SIRT5 protects against ROS-induced damage
• Desuccinylation of antioxidant enzymes enhances their activity
• SIRT5 deficiency increases oxidative stress in neurons [15]

Other Neurodegenerative Conditions

Huntington's Disease: SIRT5 is dysregulated in HD models; may affect mitochondrial function and mutant huntingtin toxicity.

Amyotrophic Lateral Sclerosis: SIRT5 levels altered in ALS models; may affect mitochondrial quality in motor neurons.

Cellular and Tissue Distribution

Brain Expression

SIRT5 is expressed in multiple brain regions:

• Cortex: Moderate expression in pyramidal neurons
• Hippocampus: High expression in CA1-3 regions and dentate gyrus
• Cerebellum: Purkinje cells show robust expression
• Substantia nigra: Dopaminergic neurons express SIRT5
• Brainstem: Moderate expression in various nuclei

• [Neurons](/entities/neurons): High expression in excitatory and inhibitory neurons
• [Astrocytes](/entities/astrocytes): Moderate expression
• [Microglia](/entities/microglia): Lower expression, increases in inflammation [14]
• Oligodendrocytes: Variable expression

Peripheral Tissues

Highest SIRT5 expression outside brain:

• Liver: Highest expression, critical for urea cycle and metabolism
• Kidney: Supports ammonia detoxification
• Heart: Cardiac metabolism regulation
• Skeletal muscle: Fatty acid oxidation
• Brown adipose tissue: Thermogenesis

Therapeutic Targeting

SIRT5 Modulators

| Strategy | Agent | Status | Mechanism |
|----------|-------|--------|-----------|
| SIRT5 activators | — | Research | Enhance desuccinylation |
| SIRT5 inhibitors | — | Research (cancer) | Block demidase activity |
| Gene therapy | AAV-SIRT5 | Preclinical | Increase SIRT5 expression |

Therapeutic Rationale

For Neurodegeneration: SIRT5 activators could:

• Restore mitochondrial function
• Reduce protein hypersuccinylation
• Protect against oxidative stress
• Improve cellular stress responses

• SIRT5 is often upregulated in cancers
• Inhibition reduces tumor cell proliferation
• Affects glutamine metabolism in cancer cells [4][16]

Research Models and Methods

Experimental Systems

• SIRT5 knockout mice: Show ammonia sensitivity, metabolic alterations
• Cellular models: Primary neurons, iPSC-derived neural cells
• Transgenic models: AD and PD models with SIRT5 manipulation

Biomarkers

• Succinylated proteins: Global succinylation as readout of SIRT5 activity
• SIRT5 expression: mRNA and protein levels in tissues
• Metabolic markers: Urea cycle intermediates, ketone bodies

Cross-Pathway Interactions

Mitochondrial Quality Control

SIRT5 intersects with multiple mitochondrial quality control pathways [13]:

• Mitophagy: Regulates PINK1/Parkin-dependent mitophagy
• Mitochondrial dynamics: Affects fission/fusion balance
• Proteostasis: Mitochondrial protein quality control

Oxidative Stress Response

SIRT5 protects against oxidative damage through [15]:

• Regulation of antioxidant enzymes
• Maintenance of NAD(P)H pool
• Modulation of redox signaling

Inflammation

SIRT5 has complex roles in neuroinflammation [14]:

• Modulates NLRP3 inflammasome
• Affects microglial activation
• May have both pro- and anti-inflammatory effects

Genetic Variation

Common Polymorphisms

• Various SNPs identified in population studies
• Some variants associated with metabolic traits
• Potential impact on SIRT5 function

Disease Associations

• Genetic variants may modulate neurodegeneration risk
• Some associations with cancer susceptibility
• Role in metabolic disease pathogenesis

See Also

• [SIRT1 Gene](/proteins/sirt1-protein)
• [SIRT2 Gene](/proteins/sirt2-protein)
• [SIRT3 Gene](/proteins/sirt3-protein)
• [Mitochondrial Dysfunction Pathway](/mechanisms/mitochondrial-dysfunction-pathway)
• [Oxidative Stress Pathway](/mechanisms/oxidative-stress-pathway)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [NCBI Gene: SIRT5](https://www.ncbi.nlm.nih.gov/gene/83737)
• [UniProt: SIRT5](https://www.uniprot.org/uniprot/Q9NXE1)
• [OMIM: SIRT5](https://www.omim.org/entry/604603)
• [Ensembl: SIRT5](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000124587)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving SIRT5 - Sirtuin 5 discovered through SciDEX knowledge graph analysis: