CHAPTER 17 – Lipoprotein structure

Publisher Summary This chapter illustrates the composition and structure of human lipoproteins. Lipoproteins are soluble complexes of proteins and lipids that transport lipids in the circulation of all vertebrates and even insects. Lipoproteins are synthesized in the liver and the intestines, arise from metabolic changes of precursor lipoproteins, or are assembled at the cell membranes from cellular lipids and exogenous lipoproteins or apolipoproteins. In the circulation, lipoproteins are highly dynamic. They undergo enzymatic reactions of their lipid components, facilitated and spontaneous lipid transfers, transfers of soluble apolipoproteins, and conformational changes of the apolipoproteins in response to the compositional changes. Finally, lipoproteins are taken up and catabolized in the liver, kidney, and peripheral tissues via receptor-mediated endocytosis and other mechanisms. Although the assembly, structure, metabolism, and receptor interactions of lipoproteins are determined by their apolipoprotein components, the most common classifications of lipoproteins are based on their hydrated density or mobility on agarose gel electrophoresis. The classification into chylomicron (CM), very low density (VLDL), low density (LDL), and high density (HDL) lipoproteins is based on their relative contents of protein and lipid that determine the densities of these lipoprotein classes. CM has only 1–2% protein whereas HDL has about 50% protein by weight.