Lipoproteins structures

FIGURE 9-1. Lipoprotein structure. Lipoproteins are a diverse group of particles with varying size and density. They contain variable amounts of core cholesterol esters and triglycerides, and have varying numbers and types of surface apolipoproteins. The apolipoproteins function to direct the processing and removal of individual lipoprotein particles. (Reprinted from LipoScience, Inc. with permission.)... 

General Considerations on the Role of Apolipoproteins in Lipoprotein Structure... 

Davis, R., Lipoprotein structure and secretion. In D. E. Vance, and J. E. Vance (eds.), Biochemistry of Lipids, Lipoproteins and Membranes. Amsterdam Elsevier Science Publishers, 1991. This chapter (14) provides an advanced discussion on the assembly and secretion of very-low-density lipoproteins. 

Scriver, C. R A. L. Beaudet, W. S. Sly, and D. Valle, The Metabolic Basis of Inherited Disease, 7th ed., vol. 1, New York McGraw-Hill, 1995. This book has an introductory chapter on lipoprotein structure and metabolism followed by many excellent chapters on disorders of cholesterol and lipoprotein metabolism. 

H. P. Shu and A. V. Nichols, Uptake of lipophilic carcinogens by plasma lipoproteins. Structure activity studies, Biochim. Biophys. Acta 665 376-384 (1981). 

Fig. 2. A model for lipoprotein structure based on the interactions between apolipopro-teins and lipid constituents. The surface monolayer is composed of phospholipids and apolipoproteins. The apoproteins contain helical regions which are amphipathic. The hydrophobic surface of the amphipathic helix interacts with the fatty acyl chains of phospholipids, and the hydrophilic surface is exposed to the aqueous environment of the polar head groups and the plasma. Adapted from Pownall et al.. (1981).

Abstract. When experimental animals are kept on an atherogenic diet the NADPH-dependent phospholipid deoxygenase in the membranes of the hepatic endoplasmic reticulum is activated and the degree of membrane oxidation is increased. Peroxide modification of microsomal membranes is attended by changes in their conformation and as a consequence, changes in the activity of membrane-bound enzymes. Proceeding from the fact that the synthesis of the components and the assembly of the supramolecular lipoprotein structure as well as cholesterol catabolism are accomplished by the enzyme systems localized in the hepatic microsomes, the role of peroxidation of the microsomal lipids in the pathogenesis of atherosclerosis is discussed. 

Cholesteric liquid-crystals and low-density lipoprotein structures... 

APOLiPOPROTEIN B AND LOW-DENSITY LIPOPROTEIN STRUCTURE IMPLICATIONS FOR BIOSYNTHESIS OF TRIGLYCERIDE-RICH LIPOPROTEINS... 

Among the problems involved in constructing a general model for vertebrate lipoprotein structure, some of the more important are the heterogeneity in size and apolipoprotein composition and the small number of examples of lipoproteins containing similar apolipoprotein composition, which can be used to validate the model. Thus, in most cases, data as elementary as the stoichiometry of the apolipoproteins cannot be included in the models (Shen et ai, 1977) or, if stoichiometry data are included, only a partial fit of the data to the model is observed (Edelstein etal., 1979). 

Lipoprotein A macromolecular particle composed of varying quantities of protein, triacylglycerol, phospholipids, cholesterol, and cholesterol esters. The lipoprotein structure has a phospholipid and free cholesterol skin surrounding a core composed of triacylglycerol and cholesterol esters, with the proteins imbedded on the surface. They serve as carriers of lipid in the circulation. 

Lipoprotein structure. The figure depicts the structure of lipoproteins, cut through the middle with a side view of the cut surface, in a general way. 

While most of the known functions of apolipoproteins are associated with their lipid-bound states, lipid-free or lipid-poor exchangeable apolipoproteins do exist in plasma and interstitial fluid, and have important metabolic roles in lipid uptake from cells, transfers between lipoproteins, structural remodeling of lipoproteins, and apolipoprotein catabolism. 

Interactions of apolipoproteins with PL are essential for the assembly of lipoproteins, stabilization of lipoprotein structures, and expression and modulation of apolipoprotein functions. The main experimental approaches for the study of apolipoprotein interactions with PL have used isolated, exchangeable apolipoproteins in conjunction with aggregated lipids dispersed in water or spread at the air-water interface. The aggregated lipid states include lipid monolayers, various types of liposomes (small unilamellar vesicles, large unilamellar vesicles, multilamellar vesicles), and emulsions. All these lipid systems consist of or include PL, especially PC. 

Investigation of the conformational adaptability of apolipoproteins during assembly with lipids and during metabolic transformations of lipoproteins in circulation. Elucidation of the conformational changes at the atomic level will be a major challenge dependent on the success of high-resolution analysis of apolipoprotein and lipoprotein structures. 

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