Alpha-galactosidase A (α-Gal A; encoded by the GLA gene is a lysosomal hydrolase that cleaves terminal alpha-galactosyl residues from glycolipids and glycoproteins. Deficiency causes Fabry disease, a lysosomal storage disorder with significant cerebrovascular and neurological manifestations.
Alpha-galactosidase A is a homodimeric lysosomal glycoprotein of ~46 kDa per subunit that catalyzes the hydrolysis of terminal α-1,4-galactosyl moieties from globotriaosylceramide (Gb3/GL-3) and related glycosphingolipids[1]. Deficiency of this enzyme, caused by X-linked mutations in GLA, results in Fabry disease, characterized by progressive accumulation of Gb3 in vascular endothelium, neurons, and visceral organs[2]. Cerebrovascular involvement (stroke, white matter lesions) and peripheral neuropathy make Fabry disease highly relevant to neurodegeneration.
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| | |
|---|---|
| Protein Name | Alpha-Galactosidase A (α-Gal A) |
| Gene | GLA |
| UniProt ID | P06280 |
| Molecular Weight | ~46 kDa (monomer), ~101 kDa (active homodimer, glycosylated) |
| Subcellular Localization | Lysosome |
| Function | Lysosomal glycoside hydrolase; cleaves α-galactosyl residues |
| EC Number | 3.2.1.22 |
α-Gal A functions as a homodimer[3]:
- TIM barrel domain (aa 32-330): (β/α)₈ barrel fold containing the active site
- C-terminal domain (aa 331-429): Antiparallel β-sheet domain involved in dimerization
- Active site: Contains catalytic residues Asp170 (nucleophile) and Asp231 (acid/base)
- N-glycosylation: Three N-linked glycosylation sites (Asn139, Asn192, Asn215) important for folding, stability, and mannose-6-phosphate receptor-mediated lysosomal targeting
α-Gal A cleaves α-galactosyl linkages through a retaining double-displacement mechanism[3]:
- Asp170 performs nucleophilic attack on the anomeric carbon of galactose
- Asp231 protonates the leaving group
- Galactosyl-enzyme intermediate is hydrolyzed by water
- Products (galactose + truncated glycolipid) are released
α-Gal A degrades glycosphingolipids in the lysosome[1]:
- Globotriaosylceramide (Gb3/GL-3): Primary substrate; accumulates in Fabry disease
- Globotriaosylsphingosine (lyso-Gb3): Deacylated form; accumulates and is directly cytotoxic
- Blood group B antigens: α-Gal A can cleave blood group B terminal galactose
- Galabiosylceramide: Alternative substrate in kidney
Beyond glycolipid catabolism, α-Gal A activity maintains[2]:
- Lysosomal function: Prevents Gb3 accumulation that disrupts lysosomal pH and enzyme activity
- Autophagy: Gb3 accumulation impairs autophagic flux
- Endothelial function: Prevents glycolipid-mediated endothelial dysfunction and vasculopathy
- Peripheral nerve function: Maintains dorsal root ganglion neuron health
Fabry disease causes significant neurological morbidity[4]:
- Small fiber neuropathy: Acroparesthesias (burning pain in hands and feet) from dorsal root ganglion Gb3 accumulation — often the first symptom
- Cerebrovascular disease: Stroke (both ischemic and hemorrhagic), white matter lesions, vertebrobasilar dolichoectasia
- Autonomic dysfunction: Hypohidrosis, gastrointestinal dysmotility, impaired heart rate variability
- Hearing loss: Sensorineural hearing loss from cochlear involvement
- Cognitive decline: White matter disease can cause progressive cognitive impairment
α-Gal A deficiency highlights shared pathways with major neurodegenerative diseases[5]:
- Lysosomal storage → autophagy impairment: Common with GBA1-related Parkinson's disease
- Endolysosomal disturbance: Parallels endosomal enlargement seen in Alzheimer's disease
- Neuroinflammation: Gb3/lyso-Gb3 activate TLR4 and NF-κB inflammatory cascades
- Vascular neurodegeneration: Cerebrovascular Gb3 accumulation causes stroke and vascular dementia
- Agalsidase alfa (Replagal): 0.2 mg/kg IV every 2 weeks
- Agalsidase beta (Fabrazyme): 1.0 mg/kg IV every 2 weeks
- Efficacy: Clears Gb3 from endothelium and some organs; limited CNS penetration
- Migalastat (Galafold): Oral small molecule that stabilizes amenable GLA mutants, improving their trafficking to lysosomes
- Plasma Gb3 and lyso-Gb3: Elevated in Fabry disease; correlate with disease severity
- α-Gal A enzyme activity: Measured in leukocytes or dried blood spots for diagnosis
| Interactor |
Type |
Function |
| Saposin B |
Activator |
Presents Gb3 substrate to α-Gal A in the lysosome |
| Mannose-6-phosphate receptor |
Trafficking |
Directs α-Gal A from Golgi to lysosome |
| Migalastat |
Pharmacological chaperone |
Stabilizes folding-competent mutants |
| LIMP-2/SCARB2 |
Lysosomal |
Lysosomal membrane protein interactor |