Glycoside Hydrolases Family 4; Alpha-glucosidases and alpha-galactosidases.
Glucosidases cleave glycosidic bonds to release glucose from oligosaccharides. Alpha-glucosidases and alpha-galactosidases release alpha-D-glucose and alpha-D-galactose, respectively, via the hydrolysis of alpha-glycopyranoside bonds. Some bacteria simultaneously translocate and phosphorylate disaccharides via the phosphoenolpyruvate-dependent phosphotransferase system (PEP-PTS). After translocation, these phospho-disaccharides may be hydrolyzed by the GH4 glycoside hydrolases such as the alpha-glucosidases. Other organsisms (such as archaea and Thermotoga maritima) lack the PEP-PTS system, but have several enzymes normally associated with the PEP-PTS operon. Alpha-glucosidases and alpha-galactosidases are part of the NAD(P)-binding Rossmann fold superfamily, which includes a wide variety of protein families including the NAD(P)-binding domains of alcohol dehydrogenases, tyrosine-dependent oxidoreductases, glyceraldehyde-3-phosphate dehydrogenases, formate/glycerate dehydrogenases, siroheme synthases, 6-phosphogluconate dehydrogenases, aminoacid dehydrogenases, repressor rex, and NAD-binding potassium channel domains, among others.