SI Antibody – Mouse Monoclonal

This gene encodes a sucrase-isomaltase enzyme that is expressed in the intestinal brush border. The encoded protein is synthesized as a precursor protein that is cleaved by pancreatic proteases into two enzymatic subunits sucrase and isomaltase. These two subunits heterodimerize to form the sucrose-isomaltase complex. This complex is essential for the digestion of dietary carbohydrates including starch, sucrose and isomaltose. Mutations in this gene are the cause of congenital sucrase-isomaltase deficiency.[provided by RefSeq, Apr 2010]

Function: Plays an important role in the final stage of carbohydrate digestion. Isomaltase activity is specific for both alpha-1,4- and alpha-1,6-oligosaccharides. Ref.7

Catalytic activity: Hydrolysis of sucrose and maltose by an alpha-D-glucosidase-type action.Hydrolysis of (1->6)-alpha-D-glucosidic linkages in some oligosaccharides produced from starch and glycogen by alpha-amylase, and in isomaltose.

Subunit structure: The resulting sucrase and isomaltase subunits stay associated with one another in a complex by non-covalent linkages.

Subcellular location: Apical cell membrane; Single-pass type II membrane protein. Note: Brush border.

Tissue specificity: Expressed in the poorly differentiated crypt cells of the small intestine as well as in the mature villous cells. Expressed at very low levels in the colon. Ref.5

Post-translational modification: The precursor is proteolytically cleaved when exposed to pancreatic proteases in the intestinal lumen.Sulfated

By similarity.

Involvement in disease: Congenital sucrase-isomaltase deficiency (CSID) [MIM:222900]: Autosomal recessive intestinal disorder that is clinically characterized by fermentative diarrhea, abdominal pain, and cramps upon ingestion of sugar. The symptoms are the consequence of absent or drastically reduced enzymatic activities of sucrase and isomaltase. The prevalence of CSID is 0.02 % in individuals of European descent and appears to be much higher in Greenland, Alaskan, and Canadian native people. CSID arises due to post-translational perturbations in the intracellular transport, polarized sorting, aberrant processing, and defective function of SI.Note: The disease is caused by mutations affecting the gene represented in this entry. Ref.8 Ref.9 Ref.10 Ref.11 Ref.12

Miscellaneous: There is a high degree of homology between the isomaltase and sucrase portions (41% of amino acid identity) indicating that this protein is evolved by partial gene duplication.

Sequence similarities: Belongs to the glycosyl hydrolase 31 family.Contains 2 P-type (trefoil) domains.