Scavenger Receptor Class B Membrane 1, also known as SR-BI plays an important role in lipid metabolism. Its main function is to mediate transfer of cholesterol between the cell surface and high density lipoprotein (HDL). HDL acts as an extracellular donor and acceptor of free and esterified Cholesterol. SR-BI also acts as a receptor for other ligands including lipoproteins, apoptotic cells and phospholipids.