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Function
a-Galactosidases are enzymes that catalyze the hydrolytic cleavage of terminal a-galactose residue from many oligosaccharides and polysaccharides. Although humans have lysosomal a-Galactosidase, the enzyme is not generally present in the human digestive tract; as a result, foods that contain raffinose, a carbohydrate broken down by a-Galactosidase, are not digested and passed through the upper intestine until they reach the lower intestine. There, a-Galactosidase producing bacteria finish the breakdown of it. Foods that contain raffinose include certain vegetables and legumes, such as beans. When the bacteria in the lower intestine ferment the carbohydrate, they release gases that can lead to flatulence. Beano is an over-the-counter supplement that contains a-Galactosidase and is promoted to prevent bloating when taken with meals containing raffinose.
Mechanism
This a-Galactosidase, along with Human a-Galactosidase, reacts via a double displacement mechanism. Asp132 acts as the nucleophile while Asp226 functions as the acid/base catalyst.
Disease
Defects in human a-GAL lead to Fabry disease, a lysosomal storage disorder characterized by the buildup of a-galactosylated substrates in the tissues. It is an X-linked inherited disorder affecting 1 in every 40,000 males characterized by chronic pain, vascular degeneration, cardiac abnormalities, and other symptoms. The disease displays distinct phenotypes correlated with the amount of residual enzymatic activity: a severe form affecting multiple organ systems including the eyes, liver, kidney, and heart; and a milder phenotype with symptoms restricted to cardiac and/or renal abnormalities. The severe phenotype generally results from a complete loss of enzymatic activity in affected individuals, whereas patients with milder phenotypes typically show some residual enzyme activity. The data base of independent Fabry disease mutations now numbers in the hundreds, from thousands of patients. Most Fabry disease patients have a single point mutation in their GLA gene coding for a-GAL, and over 400 missense and nonsense mutations have been identified in different patients. Fabry disease is a lysosomal storage disorder, a family of over 40 diseases characterized by the accumulation of a substrate in the absence of a functional lysosomal enzyme. The family includes inherited diseases such as Tay-Sachs, Sandhoff, and Gaucher diseases.
Relevance
These enzymes are found in a variety of organisms, including bacteria, fungi, plants, and animals. They often function as digestive enzymes.
Structural highlights
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