Apolipoprotein E

Apolipoprotein E (ApoE) is a 34.2 kDa glycosylated protein with 299 amino acid residues. There are three isoforms in human (apoE2, apoE3, and apoE4) due to different amino acid residues at positions 112 and 158. Apolipoprotein E is synthesized predominantly in the liver, but also by cells in the spleen, brain, lung, kidney, ovary, adrenal, and muscle tissues. Hepatic parenchyma cells are the main apoE producing cells in mammalian body, probably accounting for two thirds to three fourths of the plasma apoE . In the nervous system, Apolipoprotein E mRNA is present in neurons, astrocytes, ependymal cells, nonmyelinating Schwann cells, but not in microglia, oligodendroglia, choroidal cells, or myelinating Schwann cells. Apolipoprotein E produced by mammalian cells exists in different forms, monomers, dimers, modified, unmodified, lipid-rich, and lipid-poor, and so forth. Apolipoprotein E plays a double-role in immune responses.

Apolipoprotein E Related Areas

Cardiovascular>>Lipid Metabolism>>APOE

Apolipoprotein E Alternative Names

AD2, LDLCQ5, LPG, MGC1571[Homo sapiens]

AI255918[Mus musculus

Summaries for Apolipoprotein E

Entrez Gene summary for APOE:

Chylomicron remnants and very low density lipoprotein (VLDL) remnants are rapidly removed from the circulation by receptor-mediated endocytosis in the liver. Apolipoprotein E, a main apoprotein of the chylomicron, binds to a specific receptor on liver cells and peripheral cells. Apolipoprotein E is essential for the normal catabolism of triglyceride-rich lipoprotein constituents. The APOE gene is mapped to chromosome 19 in a cluster with APOC1 and APOC2. Defects in apolipoprotein E result in familial dysbetalipoproteinemia, or type III hyperlipoproteinemia (HLP III), in which increased plasma cholesterol and triglycerides are the consequence of impaired clearance of chylomicron and VLDL remnants. [provided by RefSeq, Jul 2008]

Wikipedia summary for Apolipoprotein E:

Apolipoprotein E (APOE) is a class of apolipoprotein found in the chylomicron and Intermediate-density lipoprotein (IDLs) that binds to a specific receptor on liver cells and peripheral cells. It is essential for the normal catabolism of triglyceride-rich lipoprotein constituents.

Human Apolipoprotein E Protein General Information

 

• Protein names: Apolipoprotein E, Short name=Apo-E
• Sequence length: 317 AA.
• Domain
• Sequence similarities: Apolipoprotein E belongs to the apolipoprotein A1/A4/E family.
• Post-translational modification: Synthesized with the sialic acid attached by O-glycosidic linkage and is subsequently desialylated in plasma. O-glycosylated with core 1 or possibly core 8 glycans. Thr-307 is a minor glycosylation site compared to Ser-308.
• Polymorphism: Three common Apolipoprotein E alleles have been identified: APOE*2, APOE*3, and APOE*4. The corresponding three major isoforms, E2, E3, and E4, are recognized according to their relative position after isoelectric focusing. Different mutations causing the same migration pattern after isoelectric focusing define different isoform subtypes. The most common isoform is E3 and is present in 40-90% of the population. Common Apolipoprotein E variants influence lipoprotein metabolism in healthy individuals.
• Subcellular location: Secreted
• Involvement in disease: Defects in Apolipoprotein E are a cause of hyperlipoproteinemia type 3 (HLPP3) [MIM:107741]; also known as familial dysbetalipoproteinemia. Individuals with HLPP3 are clinically characterized by xanthomas, yellowish lipid deposits in the palmar crease, or less specific on tendons and on elbows. The disorder rarely manifests before the third decade in men. In women, it is usually expressed only after the menopause. The vast majority of the patients are homozygous for APOE*2 alleles. More severe cases of HLPP3 have also been observed in individuals heterozygous for rare APOE variants. The influence of APOE on lipid levels is often suggested to have major implications for the risk of coronary artery disease (CAD). Individuals carrying the common APOE*4 variant are at higher risk of CAD.

General information above from UniProt

Function for Apolipoprotein E Protein

UniProtKB:

Apolipoprotein E protein mediates the binding, internalization, and catabolism of lipoprotein particles. It can serve as a ligand for the LDL (apo B/E) receptor and for the specific apo-E receptor (chylomicron remnant) of hepatic tissues.

Genatlas:

• clearance of chylomicrons, remnants and beta-VLDL from the plasma
• in the nervous system, Apolipoprotein functions as a major carrier and distributor of cholesterol and other lipids, which are essential components of neuronal membranes and myelin sheaths (Pubmed 21118811)

Homology for human Apolipoprotein E

• homolog to rattus Apoe (71.34 pc)
• homolog to murine Apoe (73.70 pc)
• homolog to APOA4

Phenotype Information for Apolipoprotein E

• Gene/Locus: APOE, AD2, LPG, LDLCQ5
• Phenotype: Alzheimer disease-2
  Hyperlipoproteinemia, type III
  Lipoprotein glomerulopathy
  Sea-blue histiocyte disease
  {Macular degeneration, age-related}
  {Myocardial infarction susceptibility}

Phenotype Information for Apolipoprotein E from OMIM (Online Mendelian Inheritance in Man)