Native Low Density Lipoprotein (LDL)

This gene product is the main apolipoprotein of chylomicrons and low density lipoproteins. It occurs in plasma as two main isoforms, apoB-48 and apoB-100: the former is synthesized exclusively in the gut and the latter in the liver. The intestinal and the hepatic forms of apoB are encoded by a single gene from a single, very long mRNA. The two isoforms share a common N-terminal sequence. The shorter apoB-48 protein is produced after RNA editing of the apoB-100 transcript at residue 2180 (CAA->UAA), resulting in the creation of a stop codon, and early translation termination. Mutations in this gene or its regulatory region cause hypobetalipoproteinemia, normotriglyceridemic hypobetalipoproteinemia, and hypercholesterolemia due to ligand-defective apoB, diseases affecting plasma cholesterol and apoB levels. [provided by RefSeq, Jul 2008]

APOB: Apolipoprotein B is a major protein constituent of chylomicrons (apo B-48), LDL (apo B-100) and VLDL (apo B-100). Apo B-100 functions as a recognition signal for the cellular binding and internalization of LDL particles by the apoB/E receptor. Defects in APOB are a cause of familial hypobetalipoproteinemia type 1 (FHBL1). A disorder characterized by highly reduced plasma concentrations of low density lipoproteins, and dietary fat malabsorption. Clinical presentation may vary from no symptoms to severe gastrointestinal and neurological dysfunction similar to abetalipoproteinemia. Defects in APOB are a cause of familial ligand-defective apolipoprotein B-100 (FDB). FDB is a dominantly inherited disorder of lipoprotein metabolism leading to hypercholesterolemia and increased proneness to coronary artery disease (CAD). The plasma cholesterol levels are dramatically elevated due to impaired clearance of LDL particles by defective APOB/E receptors. Defects in APOB associated with defects in other genes (polygenic) can contribute to hypocholesterolemia.

Protein type: Secreted, signal peptide; Carrier; Secreted

Chromosomal Location of Human Ortholog: 2p24-p23

Cellular Component: Golgi apparatus; extracellular space; endoplasmic reticulum membrane; chylomicron; cell soma; intracellular membrane-bound organelle; endoplasmic reticulum lumen; cytoplasm; early endosome; plasma membrane; extracellular region; endosome membrane; cytosol; actin cytoskeleton

Molecular Function: heparin binding; protein binding; low-density lipoprotein receptor binding; cholesterol transporter activity; phospholipid binding

Biological Process: phototransduction, visible light; lipoprotein catabolic process; response to lipopolysaccharide; response to carbohydrate stimulus; post-embryonic development; response to selenium ion; triacylglycerol catabolic process; retinoid metabolic process; transmembrane transport; nervous system development; cholesterol metabolic process; receptor-mediated endocytosis; cholesterol transport; in utero embryonic development; regulation of cholesterol biosynthetic process; response to virus; cholesterol efflux; lipoprotein metabolic process; sperm motility; cholesterol homeostasis; fertilization; lipoprotein transport; lipoprotein biosynthetic process; artery morphogenesis; spermatogenesis; triacylglycerol mobilization; blood coagulation; leukocyte migration

Disease: Hypercholesterolemia, Autosomal Dominant, Type B; Hypobetalipoproteinemia, Familial, 1