Density Lipoprotein Structure

Low-density lipoproteins contain a single molecule of apoB 100 (Knott et al., 1986) and almost no other protein therefore, they are uniquely suited to the study of the interactions between apoB and lipids. 

Lipoproteins have densities that are lower than the densities of plasma proteins, which do not contain lipids. This characteristic is used to purify and fractionate lipoproteins by sequential flotation centrifugation to 

Traditionally, human LDLs have been defined as those lipoproteins isolated in the density interval between 1.063 g/ml LDL 1.019 g/ml. This density interval may be too broad, however, because a substantial contamination with apolipoproteins other than apoB may be present on those lipoproteins at the two extremes of this density range the contaminating apolipoproteins are principally apoE (present on IDEs and HDLs at the low- and high-density extremes of this density interval, respectively) and apo(a) [present on Lp(a) at the high-density extreme]. This contamination was almost absent in the more tightly defined LDL fraction lying between 1.024 and 1.050 g/ml (Chapman et al., 1988). However, it is possible that loosely associated apolipoproteins are normally bound to LDLs in plasma and are subsequently lost during the multiple flotation steps involved in lipoprotein isolation (Mahley and Holcombe, 1977). 

By definition, the Stokes radius is obtained as the product of the anhydrous radius and the translational frictional ratio the translational frictional ratio has been measured for LDLs and found to be 1.11 (Fisher 

What is the evidence supporting the emulsion particle model for LDLs One feature that may be used to distinguish an emulsion particle from a closed bilayer vesicle is that, for an emulsion particle, all of the phospholipid should be exposed to the external medium, whereas for a bilayer vesicle, somewhat more than one-half should be exposed. Enzymatic hydrolysis of LDLs by phospholipase A2 converted all of the phosphatidylcholine and phosphatidylethanolamine to their corresponding lysophospholipids (Aggerbeck et ai, 1976), indicating that ail of the phospholipid was located at the aqueous interface at the LDL surface. In addition, P NMR studies of LDLs have demonstrated that all of the phosphate was accessible to small amounts of Pr , a rare earth probe that should not cross a bilayer because of its ionic nature (Yeagle et ai, 1978). These results agree with the emulsion particle model. 

---

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

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

Lund-Katz, S., Liu, L., Thuahnai, S.T., Phillips, M.C. 2003. High density lipoprotein structure. Frontiers in Bioscience 8 dl044-1054. 

The Sema domain consisting of about 500 amino acids is characterized by highly conserved cysteine residues that form intramolecular disulfide bonds. Crystal structures have revealed that the Sema domain folds in the manner of the (3 propeller topology which is also found in integrins or the low-density lipoprotein (LDL) receptors. Sema domains are found in semaphorins, plexins and in the receptor tyrosine kinases Met and Ron. 

Esterbauer, H., Dieber-Rotheneder, M., Waeg, G., StreigI, G. and Jurgens, G. (1990). Biochemical structural and functional properties of oxidised low density lipoprotein. Chem. Res. Tox. 3, 77-92. 

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.)... 

In addition to small organic molecules or metal ions, proteins may have other components tightly associated with them. Nucleoproteins, for instance, contain noncovalently bound DNA or RNA, as in some of the structural proteins of viruses. Lipoproteins contain associated lipids or fatty acids and may also carry cholesterol, as in the high-density and low-density lipoproteins in serum. 

An impressive example for the successful use of domino reactions for the synthesis of pharmacological lead structures was described by Paulsen et al1241 Recently, the difluoro compound 57 has been identified as highly potent inhibitor of the cholesterin-ester-transferprotein (CETP), which is responsible for a transfer of cholesterin from high-density lipoprotein (HDL) to low-density lipoprotein (LDL). This clearly results in an increase of LDL and a decrease of HDL which raise the risk of coronary heart desea-ses. The core structure of 57 is now accessible efficiently by a combination of a Mukaiyama-MichaeL... 

In the majority of cases, fluorescent labels and probes, when studied in different liquid solvents, display single-exponential fluorescence decay kinetics. However, when they are bound to proteins, their emission exhibits more complicated, nonexponential character. Thus, two decay components were observed for the complex of 8-anilinonaphthalene-l-sulfonate (1,8-ANS) with phosphorylase(49) as well as for 5-diethylamino-l-naphthalenesulfonic acid (DNS)-labeled dehydrogenases.(50) Three decay components were determined for complexes of 1,8-ANS with low-density lipoproteins.1 51 1 On the basis of only the data on the kinetics of the fluorescence decay, the origin of these multiple decay components (whether they are associated with structural heterogeneity in the ground state or arise due to dynamic processes in the excited state) is difficult to ascertain. 

In this section several recently published studies on the interaction of nonionic surfactants with a variety of biological systems, including enzymes, bacteria, erythrocytes, leukocytes, membrane proteins, low density lipoproteins and membranes controlling absorption from the gastrointestinal tract, nasal and rectal cavities, will be assessed. This is a selective account, work having been reviewed that throws light on structure-activity relationships and on mechanisms of surfactant action. 

El. Edelstein, C., Lim, C. T., and Scanu, A. M., On the subunit structure of the protein of human serum high density lipoprotein. I. A study of its major polypeptide component (Sephadex, fraction III). J. Biol. Chem. 247, 5842-5849 (1972). 

F6. Forte, G. M., Norum, K. 11., Glomset, J. A., and Nichols, A. V., Plasma lipoproteins in familial lecithin cholesterol acyltransferase deficiency structure of low- and high-density lipoproteins as recorded by electron microscopy. J. Clin. Invest. 50, 1141-1148 (1971). 

G15. Gotto, A. M., Recent studies on the structure of human serum low- and high-density lipoproteins. Proc. Nat. Acad. Sci. U.S. 64, 1119-1127 (1969). 

Scanu, A. M., Serum high-density lipoprotein effect of change in structure on activity of chicken adipose tissue lipase. Science 153, 640-641 (1966). 

Scanu, A. M., On the structure of hiunan serum low- and high-density lipoproteins. Ciba Found. Symp. IS Atherogenesis Initiative Factor, pp. 223-246 (1973). Elsevier, Amsterdam... 

Steroids that aid in muscle development are called anabolic steroids. They are synthetic derivatives of testosterone, thus have the same muscle-building effect as testosterone. There are more than 100 different anabolic steroids which, vary in structure, duration of action, relative effects and toxicities. Androstenedione, stanozolol and dianabol are anabolic steroids. They are used to treat people suffering from traumas accompanied by muscle deterioration. The use of anabolic steroid can lead to a number of dangerous side-effects, including lowered levels of high density lipoprotein cholesterol, which benefits the heart, and elevated levels of harmful low density lipoprotein, stimulation of prostate tumours, clotting disorders and liver problems. 

---