Lipoproteins insect

Chino, H. and Gilbert, L.I. (1971). The uptake and transport of cholesterol by haemolymph lipoproteins. Insect Biochem., 1, 337-347. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

In terrestrial animals, cyclodienes such as dieldrin, like other refractive lipophilic pollutants, can be excreted in their unchanged forms, notably with lipoproteins, which are exported into milk (mammals), eggs (birds, reptiles, insects), or developing... 

Tsuchida, K. and Wells, M. A. 1990. Isolation and characterization of a lipoprotein receptor from the fat body of an insect, Manduca sexta. J. Biol. Chem., 265(10) 5761-5767. 

The major lipoproteins of insect hemolymph, the lipophorins, transport diacylglycerols. The apolipo-phorins have molecular masses of -250, 80, and sometimes 18 kDa.34-37a The three-dimensional structure of a small 166-residue lipophorin (apolipophorin-III) is that of a four-helix bundle. It has been suggested that it may partially unfold into an extended form, whose amphipathic helices may bind to a phospholipid surface of the lipid micelle of the lipophorin 35 A similar behavior may be involved in binding of mammalian apolipoproteins. Four-helix lipid-binding proteins have also been isolated from plants.38 See also Box 21-A. Specialized lipoproteins known as lipovitellins... 

Chino H., Downer R. G. H. and Takahashi K. (1977) The role of diacylglycerol-carrying lipoprotein in lipid transport during insect vitellogenesis. Biochim. Biophys. Acta 487, 508-516. 

Dantuma N. P., Pijnenburg M. A., Diederen J. H. and Van der Horst D. J. (1998) Multiple interactions between insect lipoproteins and fat body cells extracellular trapping and endocytic trafficking. J. Lipid Res. 39, 1877-1888. 

Chino H. and Kitazawa K. (1981) Diacylglycerol-carrying lipoprotein of hemolymph of the locust and some insects. J. Lipid Res. 22, 1042-1052. 

Soulages J. L. and Wells M. A. (1994) Lipophorin the structure of an insect lipoprotein and its role in lipid transport in insects. Adv. Protein. Chem. 45, 371-415. 

Van Heusden M. C. and Law J. H. (1989) An insect lipid transfer particle promotes lipid loading from fat body to lipoprotein../. Lipid Res. 32, 1789-1794. 

The protein that we now refer to as lipophorin was originally referred to extensively as the insect diacylglycerol-carrying lipoprotein. It was the recognition in the 1970s that this... 

The transport of hydrocarbons by social insects can be involved in creating the hydrocarbon signature . Evidence was first obtained in the termite Zootermopsis nevaden-sis (Sevala et al., 2000). Comparison of cuticular lipids with internal and hemolymph hydrocarbons in different castes showed that, as in other species, the content was qualitatively similar. However, quantitative differences were observed between hemolymph and cuticular hydrocarbon profiles. Sevala et al. (2000) showed that hemolymph hydrocarbons were associated with a dimeric high-density lipoprotein (HDLp) lipophorin, similar to those described from other insects (see above). This lipoprotein consisted... 

Insects use camouflage coloration as a means of avoiding predation. The green color of the tobacco hornworm larvae, (Manduca sexta) can be separated into constituent blue and yellow components. The water soluble blue component is the biliprotein, insecticyanin. The yellow color is derived from lipoprotein bound carotenes. This lipoprotein, lipophorin, is the major lipid transport vehicle in insect hemolymph. In addition to transporting dietary lipid, lipophorin is also involved in the transport of lipophilic insecticides. Nearly all the recovered radioactivity in hemolymph from topically applied [14c] ddt is associated with lipophorin. Lipophorin of adult M. sexta is larger, less dense and is associated with small amounts of a third, adult specific, apoprotein. Alterations in adult lipophorin density, lipid content and apoprotein stoichiometry can be caused by injection of the decapeptide, adipokinetic hormone. 

The yellow carotene binding protein of M. sexta hemolymph is a more complicated case. Carotenes are extrerraTTy water-insoluble materials. They share this property with several other natural products including sterols, fats and hydrocarbons, all of > hich are important to insects. This property is also shared by many xenobiotics, including pesticides. Transport of hydrophobic materials within the aqueous compartments of living organisms, e.g. blood or hemolymph, is accomplished by lipoproteins. Extensive... 

It is thought that dietary carotene is transferred to the hemolymph lipoprotein, which is called lipophorin (11), at the midgut during digestion of food. It is transported to epidermal cells, where it probably associates with a different protein inside the cells. Unlike the blue component of green coloration, insects appear to be completely dependent upon dietary carotenes for the yellow component ( ). M. sexta larvae, raised on a standard laboratory diet, are distinctly blue in color, rather than green. 

What do we know about the structure and multiple functions of insect lipophorin Larval lipophorin from M. sexta (12,13), with a density of 1.15 g/ml, is comparable to the FTgh density lipoprotein... 

Table 1. Composition of High Density Lipoproteins in Insects and Man...

As one can see the question posed by the title can be answered at several levels. Pursuit of the question leads into the basic biochemistry and physiology of the insect and reveals fundamental facets of the transport of vital hydrophobic materials throughout the insect system. An understanding of the structure and functions of the lipoprotein transport vehicle may lead to a better understanding of normal physiology, as well as the mechanism for distribution of hydrophobic xenobiotics. 

It is important to understand the structure of insect cuticle before we study the cuticu-lar penetration of insecticides. Figure 6.1 shows the structure of insect integument. The integument is the outer layer of the insect, comprising the epidermis and the cuticle. The epicuticle is generally about 1 micron in thickness. It can be composed of as many as four sublayers the cement layer (outermost), the wax layer, the polyphenol layer, and the cuticu-lin layer. The epicuticle, which makes up about 5% of the total thickness of the cuticle, contains lipids, lipoprotein, and protein and, therefore, it is lipophilic. Beneath the epicuticle lies the procuticle, which comprises the exocuticle and the endocuticle. This is essentially a hydrophilic chitin-protein complex containing considerable quantities of water. The endocuticle is soft and is the major constituent of larvae and soft-bodied insects. It is composed of microfibers of chitin and protein, which may impart elasticity to the cuticle. Above this section, the exocuticle is predominant in hard-bodied insects and forms most of the cuticle in adult beetles. It is present only as a thin layer in many larvae and in the hard parts of... 

Exchangeable apolipoproteins are a class of functionally important proteins which play a key role in plasma lipoprotein metabolism. In this capacity they have been associated with several human disorders, including hyperlipidemia and cardiovascular disease (1,2). Apolipophorin-III (apoLp-III) is a model exchangeable apolipoprotein derived from the insect Manr/Mca sexta (166 residues, Mr 18,380). ApoLp-III is a major hemolymph protein in the adult life stage and... 

LIPOPHORIN THE STRUCTURE OF AN INSECT LIPOPROTEIN AND ITS ROLE IN LIPID TRANSPORT IN INSECTS... 

Vertebrate, especially mammalian, lipoproteins have been extensively studied. In the invertebrate world, only insect lipoproteins have received serious attention. Whereas vertebrates rely on a battery of lipoproteins (chylomicrons, very low-density lipoproteins, low-density lipoproteins, and high-density lipoproteins) to effect lipid transport, insects use primarily a single type of lipoprotein, lipophorin, for lipid transport. Lipophorin is both more versatile than vertebrate lipoproteins in terms of the diverse lipids it transports and more efficient than vertebrate lipoproteins in that, for the most part, it delivers lipids to tissues without being internalized and destroyed. We believe that new insights can be obtained from an understanding of insect lipoproteins, and in this article we review the current state of knowledge about the structure and metabolism of lipophorins. 

Insect lipoproteins are generally isolated by single-step ultracentrifugation in a density gradient. In all insects studied to date, the majority... 

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