LCT
Domain
The glycosyl hydrolase-1 3/region III carries the phlorizin hydrolase/glycosylceramidase activities.
The glycosyl hydrolase-1 4/region IV carries the lactase activity.
Function
Broad specificity glycosidase of the intestinal brush border membrane that hydrolyzes lactose, the main sugar in mammalian milk, to produce D-glucose and D-galactose (PubMed:12594539, PubMed:16400612, PubMed:3929764, PubMed:9762914). The mature protein is composed of two domains that catalyze the hydrolysis of beta-glucopyranosides and beta-galactopyranosides, with a preference for hydrophilic aglycones (in lactose and cellobiose) for one domain and hydrophobic aglycones (in phlorizin and glycosylceramides) for the other (PubMed:12594539, PubMed:3929764, PubMed:9762914).
Involvement in disease
Congenital lactase deficiency
COLACD
Autosomal recessive, rare and severe gastrointestinal disorder. It is characterized by watery diarrhea in infants fed with breast milk or other lactose-containing formulas. An almost total lack of LCT activity is found in jejunal biopsy material of patients with congenital lactase deficiency. Opposite to congenital lactase deficiency, also known as lactose intolerance, is the most common enzyme deficiency worldwide. It is caused by developmental down-regulation of lactase activity during childhood or early adulthood. The decline of lactase activity is a normal physiological phenomenon; however, the majority of Northern Europeans have the ability to maintain lactase activity and digest lactose throughout life (lactase persistence). The down-regulation of lactase activity operates at the transcriptional level and it is associated with a noncoding variation in the MCM6 gene, located in the upstream vicinity of LCT.
None
The disease is caused by variants affecting the gene represented in this entry.
Post-translational modifications
N-glycosylated.
Sequence Similarities
Belongs to the glycosyl hydrolase 1 family.
Tissue Specificity
Specifically expressed in small intestine.
Cellular localization
- Apical cell membrane
- Single-pass type I membrane protein
- Brush border.
Alternative names
LPH, LCT, Lactase/phlorizin hydrolase, Lactase/glycosylceramidase