<div class="infobox infobox-gene"> | | | |:---|:---| | Gene Symbol | PON3 | | Full Name | Paraoxonase 3 | | Protein Name | Arylesterase 2 | | Chromosomal Location | 7q21.3 | | NCBI Gene ID | 5446 | | OMIM ID | 605450 | | Ensembl ID | ENSG00000005421 | | UniProt ID | Q15166 | | Protein Length | 354 amino acids | | Signal Peptide | 26 amino acids (secreted) | </div>
Overview
PON3 (Paraoxonase 3) encodes a member of the paraoxonase gene family, which also includes PON1 and PON2. These enzymes are characterized by their ability to hydrolyze organophosphates and their association with high-density lipoprotein (HDL) particles. While PON1 and PON2 have been extensively studied, PON3 remains the least characterized member of the family, though emerging research reveals important roles in antioxidant defense, lipid metabolism, and cellular protection. [@rodriguezcarreno2014]
PON3 is a secreted glycoprotein that associates with HDL particles in plasma, contributing to the anti-atherogenic properties of HDL. The enzyme exhibits both paraoxonase activity (hydrolyzing the toxic organophosphate paraoxon) and arylesterase activity (hydrolyzing phenyl acetate). Additionally, PON3 has lactonase activity, enabling it to hydrolyze oxidized lipid-derived lactones and prevent the propagation of oxidative damage. These activities position PON3 as an important component of the antioxidant defense system, with implications for neurodegenerative diseases, cardiovascular disease, and metabolic disorders. [@marsillach2011]
...
PON3 — Paraoxonase 3
<div class="infobox infobox-gene"> | | | |:---|:---| | Gene Symbol | PON3 | | Full Name | Paraoxonase 3 | | Protein Name | Arylesterase 2 | | Chromosomal Location | 7q21.3 | | NCBI Gene ID | 5446 | | OMIM ID | 605450 | | Ensembl ID | ENSG00000005421 | | UniProt ID | Q15166 | | Protein Length | 354 amino acids | | Signal Peptide | 26 amino acids (secreted) | </div>
Overview
PON3 (Paraoxonase 3) encodes a member of the paraoxonase gene family, which also includes PON1 and PON2. These enzymes are characterized by their ability to hydrolyze organophosphates and their association with high-density lipoprotein (HDL) particles. While PON1 and PON2 have been extensively studied, PON3 remains the least characterized member of the family, though emerging research reveals important roles in antioxidant defense, lipid metabolism, and cellular protection. [@rodriguezcarreno2014]
PON3 is a secreted glycoprotein that associates with HDL particles in plasma, contributing to the anti-atherogenic properties of HDL. The enzyme exhibits both paraoxonase activity (hydrolyzing the toxic organophosphate paraoxon) and arylesterase activity (hydrolyzing phenyl acetate). Additionally, PON3 has lactonase activity, enabling it to hydrolyze oxidized lipid-derived lactones and prevent the propagation of oxidative damage. These activities position PON3 as an important component of the antioxidant defense system, with implications for neurodegenerative diseases, cardiovascular disease, and metabolic disorders. [@marsillach2011]
Protein Structure and Function
Structural Features
The PON3 protein (354 amino acids, ~39 kDa) shares structural features with other paraoxonase family members:
N-terminal signal peptide: 26 amino acids directing secretion
Six-bladed β-propeller: Central structural motif characteristic of the paraoxonase family
Active site: Conserved serine hydrolase active site with catalytic triad
Calcium-binding sites: Two calcium ions required for structural stability and activity
Free thiol at Cys284: Critical for enzymatic activity
Hydrophobic patch: Mediates HDL association
The enzyme is glycosylated at multiple sites, with N-linked carbohydrates contributing to its stability and function. The structure enables substrate access to the active site while maintaining proper folding and secretion. [@gupta2011]
Enzymatic Activities
PON3 exhibits multiple enzymatic activities:
Paraoxonase activity: Hydrolyzes organophosphates including paraoxon (the toxic metabolite of parathion). This activity is weaker than PON1 but still functionally relevant.
Arylesterase activity: Hydrolyzes phenyl acetate to phenol and acetate. This is considered the "natural" substrate activity and is often used for quantification.
Lactonase activity: Hydrolyzes oxidized lipid-derived lactones, particularly those formed during lipid peroxidation. This activity is critical for anti-atherogenic and neuroprotective functions. [@morin2014]
Thiolactonase activity: Specific for homocysteine thiolactone, which is toxic to endothelial cells and proteins.
Substrate Specificity
PON3 displays substrate preferences:
Best substrate: Aryl esters (phenyl acetate)
Organophosphates: Lower activity than PON1
Lactones: Similar to PON1, hydrolyzes oxidized phospholipid-derived lactones
Specificity differences: Distinct substrate profile from PON1 and PON2
Expression Pattern
Tissue Distribution
PON3 exhibits distinct tissue distribution:
Liver: Primary expression site, synthesized in hepatocytes
Plasma: Circulates associated with HDL particles
Kidney: Moderate expression
Brain: Lower expression, with regional variation
Intestine: Some expression
Lung: Detectable expression
Cell-type specificity:
Hepatocytes: Primary source of circulating PON3
Neurons: Low baseline expression, may increase under stress
Astrocytes: Expression contributes to brain antioxidant capacity
Endothelial cells: Expression may provide vascular protection
Dietary factors: High-fat diet may reduce expression
Oxidative stress: May induce expression as protective response
Developmental patterns: Age-related changes in expression
Role in Neurodegenerative Diseases
Alzheimer's Disease
PON3 is implicated in Alzheimer's disease through multiple mechanisms:
HDL-associated antioxidant activity: PON3 contributes to HDL's ability to prevent LDL oxidation. In AD, HDL function is impaired, and PON3 reduction may exacerbate oxidative damage. [@she2011]
Lipid peroxidation prevention: The lactonase activity prevents formation of toxic lipid peroxidation products that contribute to amyloid toxicity and neuronal damage.
Amyloid-beta interactions: HDL and associated proteins including PON3 may influence Aβ metabolism and clearance.
Synaptic protection: PON3 may protect synaptic membranes from oxidative damage, preserving synaptic function.
Neuroinflammation: By preventing oxidative stress, PON3 may reduce microglial activation and neuroinflammatory responses.
Studies have reported reduced PON3 expression in AD brain tissue, particularly in regions vulnerable to pathology. The enzyme's decline may contribute to the increased oxidative stress observed in AD brains. [@liu2018]
Parkinson's Disease
Dopaminergic neuron protection: The substantia nigra is particularly vulnerable to oxidative stress. PON3 may provide antioxidant protection to dopaminergic neurons. [@schrader2006]
α-Synuclein aggregation: Oxidative stress promotes α-synuclein aggregation. PON3's antioxidant activity may reduce this trigger.
Mitochondrial protection: Oxidative damage to mitochondria contributes to PD pathogenesis. PON3 may help preserve mitochondrial function.
Neuroinflammation: Reduced oxidative stress may decrease microglial activation in PD.