Apolipoprotein (Apo)

Apolipoproteins are proteins that bind lipids to form lipoproteins. They transport the lipids through the lymphatic and circulatory systems. The lipid components of lipoproteins are insoluble in water. However, because of their detergent-like (amphipathic) properties, apolipoproteins and other amphipathic molecules (such as phospholipids) can surround the lipids, creating the lipoprotein particle that is itself water-soluble, and can thus be carried through water-based circulation. Apolipoproteins also serve as enzyme cofactors, receptor ligands, and lipid transfer carriers that regulate the metabolism of lipoproteins and their uptake in tissues.There are two major types of apolipoproteins. Apolipoproteins B form low-density lipoprotein ("bad cholesterol") particles. These proteins have mostly beta-sheet structure and associate with lipid droplets irreversibly. Other apolipoproteins form high-density lipoprotein ("good cholesterol") particles.