SIRT3

Sirtuin 3
Rendering based on PDB 3GLR.
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 3GLR, 3GLS, 3GLT, 3GLU, 4BN4, 4BN5, 4BV3, 4BVB, 4BVE, 4BVF, 4BVG, 4BVH, 4FVT, 4FZ3, 4HD8, 4JSR, 4JT8, 4JT9
Identifiers
Symbols	SIRT3; SIR2L3
External IDs	OMIM: 604481 MGI: 1927665 HomoloGene: 81827 ChEMBL: 4461 GeneCards: SIRT3 Gene
Gene Ontology Molecular function • NAD+ ADP-ribosyltransferase activity • protein binding • zinc ion binding • hydrolase activity, acting on carbon-nitrogen (but not peptide) bonds, in linear amides • NAD+ binding Cellular component • mitochondrion • mitochondrial matrix • membrane Biological process • protein ADP-ribosylation • protein deacetylation • aerobic respiration • peptidyl-lysine deacetylation Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	23410	64384
Ensembl	ENSG00000142082	ENSMUSG00000025486
UniProt	Q9NTG7	Q8R104
RefSeq (mRNA)	NM_001017524	NM_001127351
RefSeq (protein)	NP_001017524	NP_001120823
Location (UCSC)	Chr 11: 0.22 – 0.24 Mb	Chr 7: 140.86 – 140.88 Mb
PubMed search
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NAD-dependent deacetylase sirtuin-3, mitochondrial also known as SIRT3 is a protein that in humans is encoded by the SIRT3 gene [sirtuin (silent mating type information regulation 2 homolog) 3 (S. cerevisiae)].^[1][2] SIRT3 is member of the mammalian sirtuin family of proteins, which are homologs to the yeast Sir2 protein. SIRT3 exhibits NAD+-dependent deacetylase activity.

Members of the sirtuin family are characterized by a sirtuin core domain and grouped into four classes, and the protein encoded by this gene is included in class I of the sirtuin family.^[1] The human sirtuins have a range of molecular functions and have emerged as important proteins in aging, stress resistance and metabolic regulation. Yeast sirtuin proteins are known to regulate epigenetic gene silencing and suppress recombination of rDNA. In addition to protein deacetylation, studies have shown that the human sirtuins may also function as intracellular regulatory proteins with mono ADP ribosyltransferase activity.

Structure

SIRT3 is a soluble protein located in the mitochondrial matrix, and contains a mitochondrial processing peptide at the N-terminus. A set of crystal structures of human SIRT3 have been solved, including an apo-structure with no substrate, a structure with a peptide containing acetyl lysine of its natural substrate acetyl-CoA synthetase 2, a reaction intermediate structure trapped by a thioacetyl peptide and a structure with the dethioacetylated peptide bond.^[3] These structures show the conformational changes induced by the two substrates required for the reaction, the acetylated substrate peptide and NAD⁺. In addition, a binding study by isothermal titration calorimetry suggests that the acetylated peptide is the first substrate to bind to SIRT3, prior to NAD⁺.

Function

Mitochondrial

Three sirtuins, SIRT3, SIRT4 and SIRT5, are located in mitochondria and have been implicated in regulating metabolic processes. Endogenous SIRT3 is a soluble protein located in the mitochondrial matrix.^[4] Overexpression of SIRT3 in cultured cells increases respiration and decreases the production of reactive oxygen species. Fasting increases SIRT3 expression in white and brown adipose tissue (WAT and BAT, respectively) and overexpression of SIRT3 in HIB1B brown adipocytes increases the expression of PGC-1α and UCP1, suggesting a role for SIRT3 in adaptive thermogenesis BAT. BAT is different from WAT because it harbors large numbers of mitochondria and is important for thermogenesis in rodents. Thermogenesis in BAT is mediated by the uncoupling protein 1 (UCP1), which induces proton leakage and thereby generates heat instead of ATP. Mechanistic insights into how SIRT3 affects thermogenesis in BAT is lacking and whether SIRT3 affects UCP1 activity directly is not known.

In addition to controlling metabolism at the transcriptional level, sirtuins also directly control the activity of metabolic enzymes. In Salmonella enterica, the bacterial sirtuin CobB regulates the activity of the enzyme acetyl-coenzyme A (acetyl-CoA) synthetase. As mentioned above, orthologs of acetyl-CoA synthetase exist in the cytoplasm (AceCS1) and in mitochondria (AceCS2) in mammals. The presence of the sirtuin deacetylase SIRT3 in the mitochondrial matrix suggests the existence of lysine acetylated mitochondrial proteins. Indeed, SIRT3 deacetylates and activates the mammalian mitochondrial acetyl-coA synthetase (AceCS2). Furthermore, SIRT3 and AceCS2 are found complexed with one another, suggesting a critical role for control of AceCS2 activity by SIRT3.

Nuclear

In addition to its reported mitochondrial function, some researchers have proposed a very small pool of active nuclear SIRT3 exists. This pool is reported to consist of the long form of SIRT3 and has been suggested to have histone deacetylase activity.^[5] The observation that SIRT3 has nuclear activity came from a report that SIRT3 protected cardiomyocytes from stress mediated cell death and that this effect was due to deacetylation of a nuclear factor, Ku-70.^[6]

Clinical significance

There is a strong association between SIRT3 alleles and longevity in males.^[7]

Aging and carcinogenesis

There is also a significant body of published literature suggesting a strong mechanistic link between mitochondrial function, aging, and carcinogenesis. ^[7]

Sirt3 functions as a mitochondrial tumor suppressor protein. Damaged and aberrant mitochondrial function, similar to gene mutations, may be an early event that ultimately leads to the development of cancers. Mice genetically altered to delete Sirt3 develop estrogen and progesterone receptor (ER/PR) positive breast mammary tumors. In tumor samples from women with breast cancer, SIRT3 expression was decreased, as compared to normal breast tissues. Thus, the Sirt3 knockout model may be used to investigate ER/PR positive breast tumor development.^[8]

References

Further reading