ATP-binding cassette sub-family G member 8 is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''ABCG8''
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.
The protein encoded by this gene is a member of the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and
intra-cellular membrane
The endomembrane system is composed of the different membranes (endomembranes) that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes ...
s. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the White subfamily. The protein encoded by this gene functions as a half-transporter to limit intestinal absorption and promote biliary excretion of
sterols
A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...
. It is expressed in a tissue-specific manner in the liver, colon, and intestine. This gene is tandemly arrayed on chromosome 2, in a head-to-head orientation with family member ABCG5. Mutations in this gene may contribute to sterol accumulation and atherosclerosis, and have been observed in patients with sitosterolemia.
A loss-of-function mutation in ABCG8 impairs the removal of sterols from cells and, in the homozygous case, leads to
sitosterolemia
Sitosterolemia, also known as phytosterolemia, is a rare autosomal recessively inherited lipid metabolic disorder. It is characterized by hyperabsorption and decreased biliary excretion of dietary sterols (including the phytosterol beta-sitoster ...
. Heterozygous individuals show slightly increased sterol absoption, normal cholesterol levels, and slightly elevated phytosterol levels.
A gain-of-function SNP rs11887534 increases the likelihood of
gallbladder disease
Gallbladder diseases are diseases involving the gallbladder and is closely linked to biliary disease, with the most common cause being gallstones (cholelithiasis).
The gallbladder is designed to aid in the digestion of fats by concentrating and ...
, especially cholesterol gallstones. This is probably because more cholesterol is pumped into the bile lumen.
Interactive pathway map
See also
*
ATP-binding cassette transporter
The ABC transporters, ATP synthase (ATP)-binding cassette transporters are a transport system superfamily that is one of the largest and possibly one of the oldest gene family, gene families. It is represented in all extant taxon, extant Phyl ...
References
Further reading
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
External links
*
*
*
ATP-binding cassette transporters
{{membrane-protein-stub