What are the functions of apolipoproteins?

Lipoproteins are particles in plasma which carry cholesterol and triglyceride. Most plasma lipoproteins are secreted by the liver or the intestine, while lipoproteins in the central nervous system are secreted largely by the glial cells. Lipoproteins are complex particles with a central core containing cholesterol esters and triglycerides surrounded by free cholesterol, phospholipids, and apolipoproteins, which facilitate lipoprotein formation and function.

Apolipoproteins or apoproteins are the polypeptides found in various types of lipoproteins. All apolipoproteins transport lipids, fulfill various functions in human lipid metabolism, and are involved in altered metabolic states or disease.

Apolipoproteins have four major functions including:
*serving a structural role,
*acting as ligands for lipoprotein receptors,
*guiding the formation of lipoproteins,
*serving as activators or inhibitors of enzymes involved in the metabolism of lipoproteins Apolipoproteins thus play a crucial role in lipoprotein metabolism

What are the functions of apolipoproteins?