Trehalase

Trehalase enzymes are hydrolytic glycosidases, produced by most forms of life (except mammals), which catalyze the reduction of trehalose (α-D-glucopyranosyl-1,1-α-D-glucopyranoside) - a non-reducing sugar and important storage carbohydrate - into glucose.

These enzymes are commonly found within brush border cells on the surface of the small intestine, and are present in most animals.

Two different trehalase enzymes have been isolated from Saccharomyces cerevisiae, and are classified according to the optimum working pH; where neutral trehalase (NT) has an optimum pH of 7.0, while that of acid trehalase (AT) is pH 4.5.

Recent studies of trehalase in S.cerevisiae have reported over 90% of AT activity is dedicated to extracellular cleavage of trehalose to glucose within the periplasmic space.

Function and classification

Hydrolysis of trehalose

One molecule of trehalose is hydrolyzed to two molecules of glucose by the enzyme trehalase. Enzymatic hydrolysis of trehalose was first observed in Aspergillus niger by Bourquelot in 1893. Fischer reported this reaction in S. cerevisiae in 1895. Since then the trehalose hydrolyzing enzyme, trehalase (α, α-trehalose-1-C-glucohydrolase, EC 3.2.1.28) has been reported from many other organisms including plants and animals. Though trehalose is not known to be produced by mammals, trehalase enzyme is found to be present in the kidney brush border membrane and the intestinal villi membranes. In the intestine the function of this enzyme is to hydrolyze ingested trehalose. Individuals with a defect in their intestinal trehalase have diarrhea when they eat foods with high trehalose content, such as mushrooms. hence, its removal may be required. It has been suggested that trehalases could play a role in defense mechanisms or the enzyme could play a role in the degradation of trehalose derived from plant-associated microorganisms.

Fungi

Two distinct trehalases have been reported from S. cerevisiae. One is regulated by cAMP-dependent phosphorylation and localized to the cytosol. The second trehalase activity is found in the vacuoles. The pH optimum of cytosolic trehalse was determined to be approximately 7.0 and is thus referred to as 'neutral trehalase' (NT); whereas the vacuolar trehalase is most active at pH 4.5 and consequently termed 'acid trehalase' (AT). These enzymes are encoded by two different genes – NTH1 and ATH1 respectively.

Cordyceps militaris uses an insect-like trehalase to break down trehalose, the main blood sugar in its silkworm host. This action causes a sharp decrease in the silkworm's blood sugar levels, which mimics starvation and triggers an increase in feeding behavior. The promotion of excessive feeding and weight gain in the host ultimately benefits the fungus by providing more resources for fruiting body formation.

Function and classification

Hydrolysis of trehalose

Fungi

References

See also