Sucrase-isomaltase
| sucrase-isomaltase (alpha-glucosidase) | |
|---|---|
| Identifiers | |
| Symbol | SI |
| Entrez | 6476 |
| HUGO | 10856 |
| OMIM | 609845 |
| PDB | 3LPO |
| RefSeq | NM_001041 |
| UniProt | P14410 |
| Other data | |
| EC number | 3.2.1.10 |
| Locus | Chr. 3 q25.2-26.2 |
Sucrase-isomaltase (EC 3.2.1.10, is a glucosidase enzyme located in on the brush border of the small intestine. Sucrase-isomaltase is a type II transmembrane glycoprotein located in the brush border of the small intestine. It has preferential expression in the apical membranes of enterocytes. The enzyme’s purpose is to digest dietary carbohydrates such as starch, glucose, and isomaltose. By further processing the broken-down products, energy in the form of ATP can be generated.
The systematic name of systematic name of sucrase-isomaltase is oligosaccharide 6-alpha-glucohydrolase. This enzyme is also known as:
This enzyme catalyses the following chemical reaction
Hydrolysis uses water to cleave chemical bonds. Sucrase-isomaltase’s mechanism results in a net retention of configuration at the anomeric center.
Sucrase-isomaltase consists of two enzymatic subunits: sucrase and isomaltase. The subunits originate from a polypeptide precursor, pro-SI. By heterodimerizing the two subunits, the sucrase-isomaltase complex is formed. The enzyme is anchored in the intestinal brush border membrane by a hydrophobic segment located near the N-terminal of the isomaltase subunit. Before the enzyme is anchored to the membrane, pro-SI is mannose-rich and glycosylated; it moves from the ER to the Golgi, where it becomes a protein complex that is N- and O- glycosylated. The O-linked glycosylation is necessary to target the protein to the apical membrane. In addition, there is a segment that is both O-linked glycosylated and Ser/Thr-rich.
Sucrase-isomaltase is composed of duplicated catalytic domains, N- and C-terminal. Each domain displays overlapping specificities. Scientists have discovered the crystal structure for N-terminal human sucrase-isomaltase (ntSI) in apo form to 3.2 Å and in complex with the inhibitor kotalanol to 2.15 Å resolution.
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