Effect of phospholipid structure on stability and survival times of liposomes in circulation

Agarwal, Kriti; Bali, Anu; Gupta, C. M.

doi:10.1016/0304-4165(86)90286-2

Cited by 20 publications

(9 citation statements)

References 30 publications

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“…Because hydrophobic interactions, due to their non-specific nature, between the sn-1 acyl chain and the enzyme [1,2,5] should not be greatly affected by replacing DPPC with DPBPC as the substrate, it is likely that the ester moiety of the sn-1 acyl chain interacts specifically, directly or indirectly, with the enzyme active site [5]. From these results, we conclude that the C1 ester moiety in DPPC could play a crucial role in its productive interactions with N. naja phospholipase A 2 , which is quite consistent with the earlier studies in which we reported slower hydrolysis of 1-O-hexadecyl-2-fatty acyl-sn-glycero-3-phosphocholines, as compared with egg phosphatidylcholines with N. naja phospholipase A 2 [18,19].…”

Section: Discussionsupporting

confidence: 91%

Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues

Puri

Arora

Gupta

1999

European Journal of Biochemistry

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To understand the role of the ester moiety of the sn-1 acyl chain in phospholipase A 2 ±glycerophospholipid interactions, we introduced an additional methylene residue between the glycerol C1 and C2 carbon atoms of phosphatidylcholines, and then studied the kinetics of hydrolysis and the binding of such butanetriol-containing phospholipids with Naja naja phospholipase A 2 . Hydrolysis was monitored by using phospholipids containing a NBD-labelled sn-2 acyl chain and binding was ascertained by measuring the protein tryptophan fluorescence. The hydrolysis of butanetriol-containing phospholipids was invariably slower than that of the glycerol-containing phospholipids. In addition, the enzyme binding with the substrate was markedly decreased upon replacing the glycerol residue with the 1,3,4-butanetriol moiety in phosphatidylcholines. These results have been interpreted to suggest that the sn-1 ester group in glycerophospholipids could play an important role in phospholipase A 2 ± phospholipid interactions.Keywords: phospholipase A 2 ; phosphatidylcholine; phospholipid conformation; butanetriol analogue.Cobra venom phospholipase A 2 is a Ca 2+ -dependent enzyme that catalyses the hydrolysis of the fatty acyl group at the sn-2 position of membrane phospholipids. It is composed of a single polypeptide chain of 119 amino acids which contains seven disulphide bonds [1]. The crystal structures of phospholipase A 2 from several sources have been determined [1±3], and the amino acids that form the enzyme catalytic site have been reported to be highly conserved [1]. Also, the structure of the catalytic surface has been shown to be exactly identical regardless of the degree of evolutionary divergence, state of oligomerization, ionic strength, or pH of the crystallization conditions [3,4].Binding of phospholipase A 2 with phosphatidylcholines involves interactions of the enzyme active site calcium with the phospholipid phosphate oxygen and the sn-2 carbonyl oxygen followed by the hydrophobic interactions between the phospholipid fatty acyl chains and the enzyme catalytic site [2±5]. Apart from the sn-2 acyl chain [5], the acyl chain at the sn-1 position also plays an important role in phospholipase A 2 ±glycerophos-pholipid interactions [6,7]. It has been reported that an increase in the hydrophobicity of the sn-1 acyl residue increases the affinity between the phospholipid molecule and the enzyme [6]. However, it is not yet known whether the ester moiety (-CO-O-) of the sn-1 acyl chain plays any role in phospholipase A 2 ± glycerophospholipid interactions. To investigate this we introduced one additional methylene residue between the glycerol C1 and C2 carbon atoms and then studied the interactions of the resulting modified phospholipids (Fig. 1) with Naja naja phospholipase A 2 . Results of these studies indicate that the sn-1 ester moiety plays an important role in binding of the enzyme with the substrate. MATERIALS AND METHODS MaterialsPhospholipase A 2 from N. naja snake venom, sn-glycero-3-phosphocholine, 6-N-(7-nitrobe...

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Section: Discussionsupporting

confidence: 91%

Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues

Puri

Arora

Gupta

1999

European Journal of Biochemistry

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“…Yet, surprisingly little evidence exists to support this fundamental hypothesis for cholesterol, a major structural component of cell membranes. Indeed with one exception (1), investigations with model membranes have found that sterol-lipid interactions do not affect membrane properties in an enantiospecific manner (2)(3)(4)(5)(6)(7)(8). These results suggest that although the physical properties of cholesterol are important for its membrane effects, the absolute configuration of cholesterol is not.…”

mentioning

confidence: 65%

Enantiospecificity of Cholesterol Function in Vivo

Crowder

Westover

Kumar

et al. 2001

Journal of Biological Chemistry

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The importance of the absolute configuration of cholesterol for its function in vivo is unknown. To directly test this question in vivo, we synthesized the enantiomer of cholesterol (ent-cholesterol) and tested its ability to substitute for natural cholesterol (nat-cholesterol) in the growth, viability, and behavior of Caenorhabditis elegans, a cholesterol auxotroph. First-generation animals grown on ent-cholesterol were viable with only mild behavioral defects. However, ent-cholesterol produced 100% lethality/arrest of their second generation progeny. Isotopically labeled ent-cholesterol incorporated into animals, indicating that its lethality was not secondary to cholesterol starvation. When mixed with nat-cholesterol, ent-cholesterol was not inert; rather, it antagonized the activity of nat-cholesterol. These results demonstrate for the first time that the absolute configuration of cholesterol, not just its physical properties, is essential for its functions in vivo.The two enantiomers of a molecule are nonsuperimposable mirror images of one another that have identical physical properties; they differ only in their absolute configuration around each chiral center and hence interact differently with chiral molecules. Sterols occur in nature as only one of the two possible enantiomers. Given this fact, enantiospecific interactions between sterols and other chiral molecules such as lipids and proteins are likely to occur and to be functionally important. Yet, surprisingly little evidence exists to support this fundamental hypothesis for cholesterol, a major structural component of cell membranes. Indeed with one exception (1), investigations with model membranes have found that sterol-lipid interactions do not affect membrane properties in an enantiospecific manner (2-8). These results suggest that although the physical properties of cholesterol are important for its membrane effects, the absolute configuration of cholesterol is not. In a broader context, whether the functions of cholesterol in vivo are enantiospecific has never been explicitly investigated.The nematode Caenorhabditis elegans requires exogenous sterols for viability. Several sterols satisfy this requirement; for example, cholesterol supports the growth, reproduction, and normal behavior of C. elegans (9 -13). Thus, C. elegans provides a good model to test the enantiospecificity of function of cholesterol in vivo. Toward this end, the non-naturally occurring enantiomer of cholesterol (ent-cholesterol) 1 was synthesized ( Fig. 1) and substituted for nat-cholesterol in cultures of C. elegans. We find that ent-cholesterol is incorporated into C. elegans but cannot perform the functions of nat-cholesterol. EXPERIMENTAL PROCEDURESMaterials ent-Cholesterol was synthesized as described (14). C. elegans were provided by the Caenorhabditis Genetics Center. Agarose was supplied by Sigma. Other reagents for the NGM culture plates and bacterial media including the natural cholesterol were supplied from Fisher Scientific. MethodsCulture Conditions-The C. eleg...

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“…7), with identical physical properties. The rationale, therefore, is that enantiomers should behave identically in the lipid bilayer (Agarwal et al, 1986a(Agarwal et al, ,1986bArnett & Gold, 1982;Ghosh et al, 1971;Guyer & Bloch, 1983;Hermetter & Paltauf, 1982;Mannock et al, 2003;Westover & Covey, 2004). On the other hand, enantioselectivity is likely to be observed in the case of a proteinaceous binding site because proteins are composed entirely of amino acids in the L-configuration.…”

Section: E Insights From Enantiomersmentioning

confidence: 99%

Mechanisms of neurosteroid interactions with GABAA receptors

Akk¹,

Covey²,

Evers³

et al. 2007

Pharmacology & Therapeutics

147

166

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Neuroactive steroids have some of their most potent actions by augmenting the function of GABA A receptors. Endogenous steroid actions on GABA A receptors may underlie important effects on mood and behavior. Exogenous neuroactive steroids have potential as anesthetics, anticonvulsants, and neuroprotectants. We have taken multiple approaches to understand more completely the interaction of neuroactive steroids with GABA A receptors. We have developed many novel steroid analogues in this effort. Recent work has resulted in synthesis of new enantiomer analogue pairs, novel ligands that probe various properties of the steroid pharmacophore, fluorescent neuroactive steroid analogues, and photoaffinity labels. Using these tools, combined with receptor binding and electrophysiological assays, we have begun to untangle the complexity of steroid actions at this important class of ligand-gated ion channel.

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Effect of phospholipid structure on stability and survival times of liposomes in circulation

Cited by 20 publications

References 30 publications

Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues

Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues

Enantiospecificity of Cholesterol Function in Vivo

Mechanisms of neurosteroid interactions with GABAA receptors

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Effect of phospholipid structure on stability and survival times of liposomes in circulation

Cited by 20 publications

References 30 publications

Probing the role of C‐1 ester group in Naja naja phospholipase A2–phospholipid interactions using butanetriol‐containing phosphatidylcholine analogues

Probing the role of C‐1 ester group in Naja naja phospholipase A2–phospholipid interactions using butanetriol‐containing phosphatidylcholine analogues

Enantiospecificity of Cholesterol Function in Vivo

Mechanisms of neurosteroid interactions with GABAA receptors

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Product

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Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues

Probing the role of C‐1 ester group in Naja naja phospholipase  A₂–phospholipid interactions using butanetriol‐containing  phosphatidylcholine analogues