Displacement of apolipophorin III from the surface of low density lipophorin by human apolipoprotein A-I

Liu, Hu; Malhotra, Veronica; Ryan, Robert O.

doi:10.1016/0006-291x(91)91878-g

Cited by 15 publications

(9 citation statements)

References 27 publications

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“…The superficial mode of binding of apoLp-III to the lipoprotein surface is functionally relevant given the reversible nature of exchangeable apolipoprotein interactions. This would facilitate dissociation from lipid surfaces without a large input of energy and is consistent with displacement studies performed by Liu et al (35) in which apoLp-III was readily displaced from the surface of low density lipophorin by human apoA-I. A similar mode of interaction has been proposed for the binding of class A amphipathic helices of apolipoproteins with the phospholipid monolayer, although a deeper penetration of the nonpolar face has been implied (36).…”

Section: Fig 2 Effect Of Apolipoproteins On Phospholipase C-inducedsupporting

confidence: 69%

Fluorescence Studies of Exchangeable Apolipoprotein-Lipid Interactions

Sahoo

Narayanaswami

Kay

et al. 1998

Journal of Biological Chemistry

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Apolipophorin III (apoLp-III) from the Sphinx moth, Manduca sexta, is an 18-kDa exchangeable apolipoprotein that reversibly associates with lipoprotein particles. In the absence of lipid, apoLp-III exists as an elongated bundle of five amphipathic ␣-helices. Upon lipid association, the protein is postulated to undergo a major conformational change, wherein the bundle opens around hinge loop regions, resulting in exposure of its hydrophobic interior. Fluorescence quenching techniques have been employed to study apoLp-III helix topography and spatial arrangement in phospholipid disc complexes and intact lipoprotein particles. Intrinsic fluorescence of the single tyrosine in apoLp-III was exploited to monitor the location of helix 5 in model disc complexes. To investigate other regions of the protein, site-directed mutagenesis was performed to introduce cysteine residues, replacing Asn-40 (helix 2, N40C) or Leu-90 (helix 3, L90C), thereby providing two mutant apoLp-IIIs, each with a single site for covalent attachment of the extrinsic fluorescent probe, N-(1-pyrene) maleimide. In the lipid-free state, pyrene-N40C-and pyrene-L90C-apoLp-III were highly accessible to the negatively charged aqueous quencher KI, yielding K sv values of 27.1 and 19.8 M ؊1 , respectively. Upon binding to the surface of a spherical lipoprotein particle, K sv values for KI decreased by about 90% for both pyrene-labeled apoLp-IIIs, indicating a significant change in the local microenvironment of the fluorophores. A lesser decrease in K sv was observed when the pyrene-labeled apoLp-IIIs were bound to phospholipid disc complexes. When spin-labeled fatty acids 5-doxylstearic acid and 12-doxylstearic acid were used as lipophilic quenchers, tyrosine and pyrene fluorescence were more effectively quenched by 5-doxylstearic acid in both phospholipid bilayer disc complexes and spherical lipoprotein particles. These data provide insight into the spatial topography of apoLp-III ␣-helices in phospholipid disc complexes and support the concept that interaction with spherical lipoprotein particles results in superficial contact of apoLp-III helical segments with the monolayer surface, providing a basis for its reversible binding ability.Plasma lipoprotein metabolism is regulated to a large extent by reversible binding of exchangeable apolipoproteins (1, 2). These amphipathic ␣-helical proteins have the ability to exist in both water-soluble and lipid-bound forms, a property which is the basis of their physiological role in lipoprotein metabolism. Apolipophorin III (apoLp-III) 1 from the Sphinx moth, Manduca sexta, is a 166-amino acid member of the exchangeable apolipoprotein family that has been well characterized (3). Structural information is available for the lipid-free form of M. sexta apoLp-III (4), as well as Locusta migratoria apoLp-III (5). Both proteins exist as globular up-and-down amphipathic ␣-helix bundles, with their polar and charged residues facing the aqueous environment and their hydrophobic residues oriented toward the protein interior....

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Section: Fig 2 Effect Of Apolipoproteins On Phospholipase C-inducedsupporting

confidence: 69%

Fluorescence Studies of Exchangeable Apolipoprotein-Lipid Interactions

Sahoo

Narayanaswami

Kay

et al. 1998

Journal of Biological Chemistry

Self Cite

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“…When compared to apoA-I, apolipophorin-III seems to interact weakly with lipid surfaces (Liu et al, 1991). In addition, the denaturation of apoLp-III resembles that of apoA-IV which is the mammalian apolipoprotein with the lowest lipid affinity (Ryan et al, 1993).…”

Section: Discussionmentioning

confidence: 97%

Effect of Diacylglycerol Content on Some Physicochemical Properties of the Insect Lipoprotein, Lipophorin. Correlation with the Binding of Apolipophorin-III

Soulages

Wells²

1994

Biochemistry

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Diacylglycerol (DG) is the main lipid component of the insect lipoprotein lipophorin. In order to study the effect of DG content on the structure and properties of lipophorin and to analyze the role of DG in the binding of apolipophorin-III (apoLp-III), an exchangeable apolipoprotein, we developed a method that allows the modification of the DG content of lipoproteins. This method employs sn-1,2-dioctanoyl glycerol (diC8-DG). The degree of incorporation of diC8-DG was determined by including [14C]-diC8DG in the incubation and subsequent purification of the diC8-DG-loaded lipophorins in a KBr gradient. The efficiency of diC8-DG loading of lipophorin is time dependent, but high levels of loading are obtained in relatively short periods of time (100% in 3-4 h). For DG loading up to about 15% (w/w), the efficiency and rate of diC8-DG loading are independent of the presence of apoLp-III. DG loading above 15% (w/w) in the absence of apoLp-III resulted in aggregation of the particles. Lipophorin particles enriched up to about 30% with diC8-DG were obtained by this procedure. When lipophorin particles were loaded with diC8-DG in the presence of apoLp-III, it was observed that binding of apoLp-III was proportional to the amount of diC8-DG incorporated into the lipophorin particle, indicating that the only requirement for apoLp-III binding to lipophorin is an increased DG content. A decrease in the degree of order of the lipid phase of the lipoproteins was observed by anisotropy of fluorescence of diphenylhexatriene as the content of diC8-DG was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…Insects possess lipoproteins called lipophorins, some of which share remarkable similarity in threedimensional structures with mammalian apoprotein E (137). For example, human apoprotein A-I can substitute for insect apolipophorin III in the constitution of lipophorins that are recognized in vivo by the putative lipophorin receptor of insect cells (72). Whether the same LDL receptor can recognize lipophorins, the insect equivalent of LDL, deserves to be examined.…”

Section: Role Of Low-density Lipoprotein Receptor In Lipid Importmentioning

confidence: 99%

The Adaptative Mechanisms ofTrypanosoma Bruceifor Sterol Homeostasis in Its Different Life-Cycle Environments

Coppens

Courtoy

2000

Annu. Rev. Microbiol.

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Bloodstream forms of Trypanosoma brucei do not synthesize sterols de novo and therefore cannot survive in medium devoid of lipoproteins. Growth of parasites is essentially supported by receptor-mediated endocytosis of low-density lipoproteins (LDLs), which carry phospholipids and cholesteryl esters. These lipids are released from internalized LDL after apoprotein B-100 is degraded by acidic thiol-proteases in the endolysosomal apparatus and then metabolized, as in mammalian cells. The LDL receptor is recycled and its expression is regulated by the sterol stores. Documented pharmacological and immunological interferences with LDL receptor-mediated lipid supply to the bloodstream forms are summarized, and the potential for new approaches to fight against these parasites is evaluated. In contrast to bloodstream forms, cultured procyclic forms can acquire sterols from both exogenous (lipoprotein endocytosis) and endogenous (biosynthesis of ergosterol) sources. The rate-limiting steps of both endocytosis (surface LDL receptor expression) and biosynthesis (3-hydroxy-3-methylglutaryl coenzyme A reductase activity) are regulated by the cellular content of sterol. These two pathways thus complement each other to yield a balanced sterol supply, which demonstrates adaptative capacities to survive in totally different environments and fine regulatory mechanisms of sterol homeostasis.

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Displacement of apolipophorin III from the surface of low density lipophorin by human apolipoprotein A-I

Cited by 15 publications

References 27 publications

Fluorescence Studies of Exchangeable Apolipoprotein-Lipid Interactions

Fluorescence Studies of Exchangeable Apolipoprotein-Lipid Interactions

Effect of Diacylglycerol Content on Some Physicochemical Properties of the Insect Lipoprotein, Lipophorin. Correlation with the Binding of Apolipophorin-III

The Adaptative Mechanisms ofTrypanosoma Bruceifor Sterol Homeostasis in Its Different Life-Cycle Environments

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