Structure and Function of the Lipolysis Stimulated Lipoprotein Receptor

Lipoproteins provide the means of transport of hydrophobic lipids in the circulation (Havel & Kane, 1995). Composed of a single monolayer of phospholipids surrounding a neutral lipid core, the primary purpose of these spherical lipid particles is to deliver two major classes of lipids – cholesterol and fatty acids (FA) to the different peripheral tissues. Cholesterol is carried in the form of free unesterified form in the phospholipid monolayer, or as cholesteryl esters (CE) in the nucleus of the lipoprotein. FA are transported in the form of triglycerides (TGs), also found in the hydrophobic core of the lipid particles along with the CE. Proteins that are amphipathic in nature are found associated with the lipoprotein and are referred to as apolipoproteins (apo). They serve as cofactors for lipid-modifying enzymes and proteins, including lipoprotein lipase, hepatic lipase, lecithin-cholesterol acyltransferase and cholesteryl-ester transfer protein. Apolipoproteins also serve as ligands that bind to specific sites of lipoprotein receptors, providing a means by which the lipoproteins are bound and then internalized through endocytosis via these receptors located on cell surface membranes.