Apolipoprotein E/APOE4 Protein, Human (HEK293, His)

Apolipoprotein E (APOE) is a lipid-associated protein that primarily facilitates lipoprotein-mediated lipid transport between organs through plasma and interstitial fluids. As a core component of plasma lipoproteins, APOE participates in their production, conversion, and clearance. This amphipathic molecule interacts with both lipoprotein core lipids and the aqueous plasma environment, binding to chylomicrons, chylomicron remnants, VLDL, and IDL while showing preferential affinity for HDL. APOE engages with cellular receptors including LDLR, LRP1/LRP2/LRP8, and VLDLR to mediate cellular uptake of APOE-containing lipoprotein particles. Its heparin-binding activity enables interaction with cell-surface heparan sulfate proteoglycans, facilitating lipoprotein capture and receptor-mediated endocytosis. A key function involves hepatic clearance of chylomicrons, VLDL, and HDL. APOE contributes to VLDL biosynthesis in the liver and subsequent peripheral tissue uptake for triglyceride delivery and energy storage. It maintains systemic lipid homeostasis by coordinating inter-tissue lipid distribution and participates in reverse cholesterol transport via HDL biogenesis (with ABCA1) and hepatic HDL uptake. In the central nervous system, APOE regulates lipid transport, neuronal survival, and sprouting. The protein also modulates innate/adaptive immune responses (by similar) through interactions with LILRB4 and may influence transcription via a cholesterol-independent mechanism activating MAP3K12 and non-canonical MAPK signaling to enhance AP-1-mediated APP expression.