PEX16 (Peroxisome Biogenesis Factor 16), also known as peroxin-16, encodes an essential peroxisomal membrane protein critical for early stages of peroxisome biogenesis. Peroxisomes are ubiquitous single-membrane organelles that perform vital metabolic functions including fatty acid beta-oxidation, plasmalogen synthesis, and reactive oxygen species metabolism. PEX16 specifically plays a central role in peroxisome membrane assembly by serving as a docking site for peroxisomal membrane proteins (PMPs) and facilitating the initial membrane formation step[@eberhart2015].
Mutations in PEX16 cause peroxisome biogenesis disorders (PBDs), a group of severe autosomal recessive diseases characterized by profound developmental defects, neurological impairment, and early lethality. Beyond these classical peroxisome disorders, PEX16 dysfunction has been increasingly implicated in common neurodegenerative diseases including Alzheimer's disease and Parkinson's disease, where peroxisomal dysfunction contributes to disease pathogenesis[@smith2013].
| Property |
Value |
| Gene Symbol |
PEX16 |
| Full Name |
Peroxisome Biogenesis Factor 16 |
| Chromosomal Location |
11p11.2 |
| NCBI Gene ID |
5494 |
| OMIM ID |
603460 |
| Ensembl ID |
ENSG00000121653 |
| UniProt ID |
Q9Y5Y5 |
| Encoded Protein |
Peroxin-16 |
| Protein Family |
PEX proteins, peroxisome biogenesis factors |
| Protein Length |
336 amino acids |
| Subcellular Location |
Peroxisomal membrane |
Peroxisomes are dynamic organelles present in virtually all eukaryotic cells:
Key Functions:
- Fatty acid β-oxidation: Very long-chain fatty acids, dicarboxylic acids, pipecolic acid
- Plasmalogen synthesis: Ether phospholipids critical for myelin
- Hydrogen peroxide metabolism: Via catalase
- Bile acid synthesis: Primary pathway in liver
- Glycolysis: In some organisms
Peroxisome Characteristics:
- Single limiting membrane
- Matrix proteins imported post-translationally
- Diameter: 0.1-1 μm
- Number per cell: 100-1000
Peroxisomes can arise from two pathways[@watkins2015]:
- De novo biogenesis: From endoplasmic reticulum
- Growth and division: From existing peroxisomes
PEX16 plays a critical role in both pathways, particularly in membrane formation.
¶ PEX16 Structure and Function
PEX16 is an integral peroxisomal membrane protein with:
- N-terminal cytosolic domain: May interact with cytosolic factors
- Membrane-spanning regions: Multiple transmembrane domains
- C-terminal intraperoxisomal domain: Interacts with other peroxins
¶ Functional Domains
Membrane Anchors:
- Two or more transmembrane domains anchor PEX16 in the peroxisomal membrane
- Orientation exposes functional domains to cytosol and matrix
PMP Docking Site:
- PEX16 serves as a docking station for newly synthesized PMPs
- Facilitates import of membrane proteins
PEX16 functions at multiple stages[@mullen2016]:
- Initial membrane formation: Directs ER-derived membrane vesicles
- PMP import: Docks precursor PMPs for insertion
- Peroxisome proliferation: Supports division and growth
De Novo Biogenesis Pathway:
ER membrane → PEX16-containing vesicles → Peroxisome membrane → Mature peroxisome
Peroxisomal dysfunction is increasingly recognized in AD pathogenesis[@kovacs2016]:
Plasmalogen Deficiency:
- Peroxisomes are the primary site of plasmalogen synthesis
- Plasmalogens are essential for neuronal membrane integrity
- AD brain shows significant plasmalogen reductions
- PEX16 dysfunction would exacerbate this deficit
β-Oxidation Impairment:
- Peroxisomal fatty acid oxidation removes neurotoxic species
- Impaired oxidation leads to lipid accumulation
- Contributes to neuronal dysfunction
Reactive Oxygen Species:
- Catalase in peroxisomes detoxifies hydrogen peroxide
- Peroxisomal dysfunction increases oxidative stress
- Promotes neurodegeneration
PEX16 in AD:
- PEX16 expression altered in AD brain
- May contribute to peroxisomal deficits
- Therapeutic targeting could be beneficial
Peroxisomes connect to multiple aspects of PD pathogenesis:
Fatty Acid Metabolism:
- Peroxisomal β-oxidation processes long-chain fatty acids
- Altered lipid metabolism in PD brain
- PEX16 dysfunction would compound deficits
Dopaminergic Neuron Vulnerability:
- Dopaminergic neurons have high peroxisome content
- Sensitive to peroxisomal dysfunction
- May be affected by PEX16 alterations
PEX2/PEX10 Connection:
- Other peroxins implicated in PD
- Shared pathway with PEX16
- Combined effects on neurodegeneration
Lipid Homeostasis:
- Peroxisomes regulate cellular lipid composition
- Dysfunction disrupts membrane properties
- Affects neuronal function and survival
Inflammation:
- Peroxisomes modulate inflammatory responses
- Dysfunction promotes neuroinflammation
- Contributes to disease progression
| Protein |
Interaction Type |
Functional Consequence |
| PEX3 |
Direct binding |
Membrane assembly |
| PEX19 |
Direct binding |
PMP targeting |
| PEX10 |
Functional connection |
Import complex |
| PEX2 |
Functional connection |
Import complex |
| PEX12 |
Functional connection |
Import complex |
PEX16 interfaces with the peroxisomal import machinery:
- PEX19: Cytosolic chaperone for PMPs
- PEX3: Membrane receptor for PMP import
- PEX10/PEX12: ubiquitin ligase complex
PEX16 is expressed in most tissues:
| Tissue |
Expression Level |
| Liver |
High |
| Brain |
High |
| Kidney |
High |
| Muscle |
Moderate |
| Heart |
Moderate |
In the brain, PEX16 shows regional variation:
| Brain Region |
Expression Level |
Relevance |
| Cerebral Cortex |
High |
Cognitive function |
| Hippocampus |
High |
Memory |
| Cerebellum |
Moderate |
Motor function |
| Substantia Nigra |
Moderate |
PD relevance |
- Neurons: High peroxisome content
- Astrocytes: Peroxisomes for lipid metabolism
- Oligodendrocytes: Plasmalogens for myelin
- Microglia: ROS metabolism
PEX16 mutations cause severe PBDs:
Zellweger Syndrome Spectrum:
- Most severe: Zellweger syndrome
- Intermediate: Neonatal adrenoleukodystrophy (NALD)
- Mildest: Refsum disease
Clinical Features:
- Severe developmental delay
-Characteristic facial features
- Hepatic dysfunction
- Neurological impairment
- Early lethality
Inheritance: Autosomal recessive
Prevalence: Rare (1:100,000 to 1:150,000)
Carrier frequency: Low in general population
Diagnosis: Enzymatic testing, genetic analysis
Gene Therapy:
- Viral vector delivery of functional PEX16
- Under investigation for PBDs
Small Molecule Approaches:
- Enhancers of peroxisome function
- Targeting downstream metabolic pathways
Combination Approaches:
- Gene therapy plus metabolic support
- Enzyme replacement where applicable
- BBB penetration: CNS delivery needed
- Early intervention: Treatment before irreversible damage
- Gene-specific effects: Different mutations, different severity
Peroxisomes are dynamic organelles:
- Biogenesis: New peroxisome formation
- Growth: Import of matrix proteins
- Division: Binary fission
- Autophagy: Pexophagy for quality control
PEX16 participates in the biogenesis and division processes.
Pexophagy:
- Damaged peroxisomes removed via autophagy
- Recognition and targeting mechanisms
- PEX16 alterations may affect quality control
Peroxisomes oxidize:
- Very long-chain fatty acids (>C22)
- Branched-chain fatty acids
- Dicarboxylic acids
- Prostaglandins
PEX16 function affects this capacity.
Peroxisomes synthesize:
- Ether phospholipids (plasmalogens)
- Critical for myelin structure
- Affected in PBDs and AD
- What regulates PEX16 expression in different tissues?
- How does PEX16 coordinate peroxisome assembly?
- Can targeting PEX16 benefit neurodegenerative disease?
- PEX16 in iPSC models
- Gene therapy development
- Peroxisome-targeted therapeutics
- Eberhart et al., Peroxisome biogenesis and human disease (2015)
- Watkins et al., PEX genes and peroxisome biogenesis disorders (2015)
- Ito et al., Peroxisome biogenesis disorders (2011)
- Smith et al., The role of peroxisomes in metabolism and neurodegeneration (2013)
- Kovacs et al., Peroxisomes in Alzheimer's disease and Down syndrome (2016)
- Ivansson et al., PEX16 in peroxisome membrane assembly (2010)
- Hille et al., Peroxisomal disorders (1985)
- Moser et al., Peroxisome biogenesis disorders (1999)
- Stowers et al., PEX16: a peripheral peroxisomal membrane protein (2000)
- Mullen et al., Peroxisome biogenesis and membrane protein insertion (2016)
- Anton et al., Peroxisomes and neurodegenerative disease (2008)
- Kovacs et al., Peroxisome deficiency and dysfunction in aging brain (2014)
- Cho et al., PEX16 deficiency and peroxisome dynamics (2013)
- Jansen et al., Biochemical and molecular aspects of peroxisome biogenesis (2011)
- Waterham et al., Peroxisome biogenesis disorders (2017)