Lysosomal alpha-glucosidase
EC=3.2.1.20
Alternative name(s):
Acid maltase
Aglucosidase alfa
Cleaved into the following 2 chains:
76 kDa lysosomal alpha-glucosidase
70 kDa lysosomal alpha-glucosidase
Function
Essential for the degradation of glygogen to glucose in lysosomes.
Catalytic activity
Hydrolysis of terminal, non-reducing (1->4)-linked alpha-D-glucose residues with release of alpha-D-glucose.
Subcellular location
Lysosome. Lysosome membrane Ref.14.
Post-translational modification
The different forms of acid glucosidase are obtained by proteolytic processing.
Phosphorylation of mannose residues ensures efficient transport of the enzyme to the lysosomes via the mannose 6-phosphate receptor.
Polymorphism
There are three common alleles of GAA: GAA*1, GAA*2 and GAA*4. The sequence shown is that of allele GAA*1, which is the most common. Alleles GAA*2 and GAA*4 are much rarer.
Involvement in disease
Defects in GAA are the cause of glycogen storage disease type 2 (GSD2) [MIM:232300]; also called acid alpha-glucosidase (GAA) deficiency or acid maltase deficiency (AMD). GSD2 is a metabolic disorder with a broad clinical spectrum. The severe infantile form, or Pompe disease, presents at birth with massive accumulation of glycogen in muscle, heart and liver. Cardiomyopathy and muscular hypotonia are the cardinal features of this form whose life expectancy is less than two years. The juvenile and adult forms present as limb-girdle muscular dystrophy beginning in the lower limbs. Final outcome depends on respiratory muscle failure. Patients with the adult form can be free of clinical symptoms for most of their life but finally develop a slowly progressive myopathy.
