Changes in lipoprotein composition during larval-pupal metamorphosis of an insect, Manduca sexta

Isolation and characterization of a hemocyte aggregation inhibitor from hemolymph of Manduca sexta larvae

A protein that inhibits hemocyte aggregation has been isolated from hemolymph of Manduca sexta larvae and named hemocyte aggregation inhibitor protein (HAIP). HAIP has a M(r) = 50,000, pI = 8.5, and contains 7% carbohydrate. It is present at 230 +/- 20 micrograms/ml in hemolymph of day 3 fifth instar larvae. Antibodies to HAIP do not cross-react with M. sexta hemolin, which is similar in size and charge and also inhibits hemocyte aggregation. HAIP and hemolin have some similarity in amino acid composition and NH2-terminal sequence, but are different in overall secondary structure, as determined by CD spectroscopy. The concentration of HAIP in hemolymph is not affected by injection of larvae with bacteria. A protein of approximately 50,000 daltons that reacts with antibody to M. sexta HAIP is present in hemolymph of Bombyx mori, Heliothis zea, and Galleria mellonella. Although the function of HAIP in vivo is not yet clear, it may have a role in modulating adhesion of hemocytes during defensive responses.

Immunocytochemical localization of a follicle specific protein of the hawkmoth Manduca sexta

A follicle specific protein (FSP-I) from the hawkmoth Manduca sexta, has been localized in developing follicles by immuno-fluorescence and immuno-gold labeling techniques. At the light microscopical level, the protein was demonstrated to be present in both the basolateral and apical parts of follicular epithelial cells, as well as in clearly defined, spherical compartments in the cortex of the developing oocyte. Immuno-gold labeling at the electron microscopical level revealed the localization of FSP-I in endoplasmic compartments of the follicular epithelial cells, in the extracellular matrix of the follicle and in endocytic compartments of the oocyte. Our results indicate that M. sexta FSP-I is synthetized and secreted by the follicular epithelial cells, after which it is taken up by the developing oocyte through endocytic routes.

Characterization and identification of a lipoprotein lipase from Manduca sexta flight muscle

Lipoprotein lipase (LpL) activity in Manduca sexta flight muscle tissue was measured using in vivo radiolabeled lipophorin as a substrate. LpL hydrolyses diacylglycerol in the low density lipophorin (that occurs during flight) at a higher rate than diacylglycerol in the high density lipophorin (present in the resting insect). LpL has a pH-optimum of 7.5 and is less sensitive to NaCl than mammalian LpL. LpL is inhibited by bovine albumin and chicken ovalbumin. LpL is inhibited by the serine protease inhibitors diisopropylfluorophosphate (DFP) and phenylmethanesulfonyl fluoride (PMSF), which indicates the presence of an active site serine similar to mammalian LpL. Flight muscle LpL shows affinity for immobilized copper as well as for immobilized heparin. Using radiolabeled DFP, a protein of 37 kDa was identified (after SDS-PAGE) as the DFP-binding protein in a partially purified preparation of LpL. This 37 kDa protein is proposed to be the LpL or a subunit thereof.

Effects of parasitism by the braconid wasp Cotesia congregata on host hemolymph proteins of the tobacco hornworm, Manduca sexta

Parasitism by the braconid wasp Cotesia congregata causes major alterations in the hemolymph proteins of host tobacco hornworm larvae. Earlier studies showed that the total amount of hemolymph protein is reduced during parasitism, beginning almost immediately after the host is parasitized. Simultaneously, parasitism induces synthesis of large amounts of novel proteins that appear in the blood as early as 1-2 h post-parasitization. The present report confirms earlier studies describing the presence of novel proteins in last instar hosts, and also characterizes the effects of parasitism in altering the titers of several endogenous host hemolymph proteins normally produced by the fat body and other tissues. Analysis of hemolymph plasma using SDS-PAGE and densitometry, as well as immunodiffusion assays, showed that in terminal stage fifth instar host larvae, the titers of serpins and arylphorin were dramatically reduced relative to the levels of these proteins detected in nonparasitized gate II fifth instar larvae of the same age. The relative differences between parasitized and nonparasitized larvae increased with time following ecdysis to the fifth instar, so that the day 4 nonparasitized larvae had arylphorin titers of c. 30 mg/ml, whereas parasitized day 4 larvae with newly emerged wasps had only one sixth that amount of storage protein circulating in the hemolymph. Similarly, in nonparasitized larvae the hemolymph serpin concentration increased from c. 200 micrograms/ml (on day 0) to > 600 micrograms/ml (on day 4) in prewandering gate II larvae, but in parasitized larvae the hemolymph serpin concentration was maintained in the range of 100-200 micrograms per ml hemolymph until the pharate third instar parasites emerged from the host larva on day 4. In contrast, the level of hemolymph lipophorin was unaffected by parasitism, and lipophorin increased from c. 1.3 to > 3 mg/ml during the time interval between days 0 and 4 in both nonparasitized and parasitized larvae. Hemolymph titers of insecticyanin also were not significantly different in parasitized vs nonparasitized larvae, and in both types of larvae the concentration of this pigment decreased by c. 50% during the same time interval when lipophorin was increased significantly. Instead of causing a generalized inhibition of host hemolymph protein synthesis, parasitism causes a complex array of changes in the hemolymph protein profile of Manduca sexta, possibly via the mediation of hormonal modulators of host protein synthesis, or transcriptional or translational regulation of host gene expression by factors associated with the polydnavirus or molecules secreted by the parasites.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetric and spectroscopic studies of the interaction of Manduca sexta apolipophorin III with zwitterionic, anionic, and nonionic lipids

The nature of the interaction of apolipophorin III (apoLp-III) from the insect Manduca sexta with a variety of zwitterionic and anionic phospholipids and with several nonionic glycolipids was investigated by differential scanning calorimetry (DSC) and 31P-NMR spectroscopy. Monoglucosyldiacylglycerol, phosphatidylethanolamine, and phosphatidic acid (pH 7.2) appear to exhibit the weakest interaction with apoLp-III. DSC studies revealed that the gel/liquid-crystalline phase transition of these lipids is little affected by the binding of apoLp-III. Diglucosyldiacylglycerol, phosphatidylcholine (PC), phosphatidylserine, and phosphatidic acid (pH congruent to 8.8) seem to exhibit somewhat stronger interactions with apoLp-III. The binding of apoLp-III to these lipids induces the formation of lipid domains which melt less cooperatively and at higher temperatures than do the pure lipid dispersions, while having little effect on the melting enthalpy of lipid hydrocarbon chains. Phosphatidylglycerol (PG) and phosphatidic acid (pH > 9.3) appear to exhibit the strongest interactions with apoLp-III. The binding of apoLp-III to these lipids severely disrupts their bilayer structure, resulting in marked reductions in the cooperativity and enthalpy of the gel/liquid-crystalline phase transition of the lipids. Studies of binary mixtures of PC and PG indicate that such bilayer-disrupting interactions only occur in the presence of nonphysiologically high concentrations of PG. The binding of apoLp-III to binary mixtures of diacylglycerol and zwitterionic phospholipid has little effect on the chain-melting or the bilayer/nonbilayer phase transitions of these lipids, but it appears to promote the retention of water at the surface of the lipid aggregate. Our results indicate that the binding of apoLp-III to lipid bilayers is mediated primarily through polar and/or ionic interactions at the lipid bilayer surface. Our results also suggest that the interaction of apoLp-III with lipid bilayers promotes the hydration of their surfaces, a property which is consistent with the proposed in vivo functions of this protein.

Protein and lipoprotein uptake by developing oocytes of the hawkmoth Manduca sexta. An ultrastructural and immunocytochemical study

The ultrastructure of developing Manduca sexta oocytes is described with respect to the endocytic pathway for protein incorporation. Three major (lipo) protein components of mature M. sexta eggs, lipophorin, vitellogenin and microvitellogenin, were localized along this pathway by immuno-fluorescence and immuno-gold labeling techniques. Labeling of the antigens was observed in the extracellular spaces of the follicle. In those cases where fixation and en bloc staining procedures did not destroy antigenicity, antigens were detected in coated pits and coated vesicles near the plasma membrane of the oocyte. All three antigens were demonstrated to be present in endosomes in the cortex of the oocyte. Both the morphology and the labeling pattern of the endosomes indicate that this organelle is a compartment of uncoupling of receptor and ligand. Tubular elements at the surface of the endosome, interpreted to be involved in the recycling of receptors and membrane to the oocyte surface, were not labeled. Strong labeling of lipophorin, vitellogenin and microvitellogenin was observed in the developing yolk bodies, the main protein storage compartment of the oocyte. The uptake and storage of hemolymph proteins and lipoproteins by M. sexta oocytes is discussed in comparison with other insect and vertebrate endocytic systems.

A turbidimetric assay of lipid transfer activity

A novel method to assay insect plasma lipid transfer particle (LTP) activity has been developed that employs insect high density lipophorin (HDLp) and human low density lipoprotein (LDL) as donor/acceptor substrate particles. At a 3:1 or greater HDLp:LDL protein ratio, LTP-mediated net vectorial transfer of diacylglycerol from lipophorin to LDL produces destabilized LDL particles that aggregate, causing sample turbidity. Turbidity was measured spectrophotometrically as a function of absorbance at 340 nm. After an initial lag phase, lipoprotein sample turbidity increased as a function of reaction time and LTP concentration. Saturation was observed at longer times or higher LTP concentrations, indicating that a reaction end point had been reached. As the substrate HDLp concentration was increased relative to LDL, a saturable increase in LTP-induced lipoprotein sample turbidity was observed. When the LDL concentration was increased relative to HDLp, however, there was an initial production of turbidity but at higher concentrations the sample did not develop turbidity. Reaction progress was also dependent on temperature over the range 0-37 degrees C. Taken together the results are consistent with the concept that LTP-mediated diacylglycerol transfer from HDLp to LDL creates unstable product LDL particles that aggregate. The assay method is advantageous because it employs relatively abundant, natural lipoprotein substrates, does not require prelabeling of donor lipid particles with radioactive or fluorescent lipids, and does not require separation of donor and acceptor after incubation. This is the first description of a lipid transfer assay that can be measured spectrophotometrically.

Role of lipid transfer particle in transformation of lipophorin in insect oocytes

Oocyte development in Manduca sexta involves the deposition of large amounts of lipoprotein-derived lipid. One source of this lipid is hemolymph high-density lipophorin-adult (HDLp-A) which, upon entry into the oocyte, is transformed into a lipid and apolipophorin III deficient product particle, egg very-high- density lipophorin (VHDLp-E; density = 1.24 g/ml; Kawooya et al. (1988) J. Biol. Chem. 263, 8740-8747). An in vitro model of this transformation has been established using human low-density lipoprotein (LDL) as acceptor of HDLp-A associated lipid in a reaction catalyzed by isolated M. sexta hemolymph lipid transfer particle (LTP). Facilitated vectorial net transfer of lipid from HDLp-A to LDL resulted in formation of a very-high-density lipophorin (VHDLp) product with a density and apolipoprotein content similar to that of VHDLp-E. Lipid was found to comprise 25% of the VHDLp particle mass, whereas over 50% of HDLp-A mass is lipid. Based on these observations it was hypothesized that a lipid transfer factor may be present in M. sexta oocytes and function in the transformation of HDLp-A to VHDLp-E in vivo. Transfer activity was present in the buffer soluble fraction of oocyte homogenates and purification of the active material revealed a catalyst with electrophoretic and immunological properties identical to hemolymph LTP. Incubation of 125I-HDLp-A with an M. sexta oocyte homogenate resulted in transformation of the radiolabeled lipoprotein to a density corresponding to that of VHDLp-E. When the incubation media was preincubated with anti-LTP IgG this conversion was inhibited to a large extent. Inhibition was relieved, however, by addition of exogenous LTP. The results provide the first demonstration of M. sexta LTP in a tissue other than hemolymph and support the concept that LTP-catalyzed lipid transfer plays an integral role in the conversion of HDLp-A to VHDLp-E in vivo.

Lipid transfer particle-catalyzed transfer of lipoprotein-associated diacylglycerol and long chain aliphatic hydrocarbons

Following injection of [1-14C]acetate into the sphinx moth, Manduca sexta, radiolabel was incorporated into lipid components of the major hemolymph lipoprotein, adult high density lipophorin (HDLp-A). Analysis of the labeled lipids by thin layer chromatography and radiochromatogram scanning revealed incorporation of radioactivity into the diacylglycerol (DAG) and hydrocarbon components as well as a third lipid fraction of unknown identity. Lipid transfer experiments were carried out using 14C-lipid HDLp-A and human low density lipoprotein (LDL) as donor/acceptor substrates and M. sexta lipid transfer particle (LTP) as catalyst. In control incubations lacking LTP, nearly all of the radiolabeled lipid remained associated with HDLp-A. LTP, however, induced a time-dependent vectorial transfer of radiolabeled lipid from HDLp-A to LDL. Lipid analysis of the LDL fraction, reisolated following the transfer reaction, revealed that labeled lipid components originally associated with HDLp-A were present in the acceptor LDL particles. The recovery of radiolabeled hydrocarbon associated with LDL demonstrates the capacity of LTP to facilitate transfer of these long chain, extremely hydrophobic, lipids and suggests LTP may function as a mediator of hydrocarbon transport and metabolism in vivo. When acceptor LDL particles were analyzed prior to complete transfer of HDLp-A-associated lipid it was observed that DAG was transferred preferentially during the initial stages of the reaction after which hydrocarbon transfer increased. This result suggests that LTP may have a lipid substrate preference for DAG versus hydrocarbon. Alternatively the observed preference for DAG may be a function of the relative accessibility of the substrates within the donor lipoprotein. In other experiments it was demonstrated that, unlike other lipids associated with HDLp-A, free fatty acid spontaneously transfers to LDL in the absence of lipid transfer catalyst.

Purification of insect vitellogenin and vitellin by gel-immobilized ferric chelate

Vitellogenin and vitellin of Manduca sexta and some other insect species were purified by immobilized metal ion affinity chromatography. Ferric ion was chosen as the immobilized metal ion. Agarose-bound carboxymethylpicolylamine was used as the chelating adsorbent for the ferric ion. Vitellogenin and vitellin, both phosphorylated lipoproteins, were shown to bind specifically to the iron. The general applicability of immobilized ferric ion affinity chromatography for the purification of insect vitellogenin and vitellin is suggested.

Lipophorin from the tsetse fly, Glossina morsitans morsitans

1. Lipophorin was isolated from the haemolymph of adult tsetse fly, Glossina morsitans morsitans, by ultracentrifugation in a potassium bromide density gradient. 2. The tsetse fly lipophorin (Mr congruent to 600,000) has a density of congruent to 1.11 g/ml and consists of two apoproteins, apolipophorin-I (apoLp-I, Mr congruent to 250,000) and apolipophorin-II (apoLp-II, Mr congruent to 80,000), both of which are glycosylated as shown by staining with periodate-Schiff reagent. The protein complex is composed of 49% protein and 51% lipids. 3. The finding of lipophorin in tsetse fly haemolymph suggests that, although these flies primarily utilize proline for their energy needs, there is an active transport mechanism for the supply of lipid requirements.

Serum high-density lipoproteins in the crab, Cancer antennarius--III. Density-gradient profiles and lipid composition of subclasses

1. Prestaining the serum total lipoprotein (LP) fraction and density-gradient ultracentrifugation revealed up to five LPs, all in the high-density class (HDL; 1.187 greater than d greater than 1.080 g/ml). These are group-designated as HDL1, HDL2 and HDL3, lowest to highest buoyant density, respectively. The number and precise density of the LPs varied with individual crab and were not gender specific. 2. The percentage of total mass due to triacylglycerides was progressively higher from HDL1 and HDL3, whereas that of phospholipids, cholesterol and combined fat was progressively lower. The percentage mass of combined fat was higher in females than males. 3. As in hemolymph, the LP of eggs was entirely HDL; instances of each HDL subclass were seen, but HDL3 was predominant. Compared with serum HDL, egg HDL was strikingly low in triacyglyceride mass and relatively high in protein. 4. Hemolymph HDL titers of individual females varied independently with egg size through most of the year, but was positively correlated with the egg size in October to December when 2-3-fold increases in HDL titer occur in the female population.

Adipokinetic hormone controls lipid metabolism in adults and carbohydrate metabolism in larvae of Manduca sexta

The peptide hormone which controls activation of fat body glycogen phosphorylase in starving larvae of Manduca sexta was isolated from larval corpora cardiaca and sequenced by FAB tandem mass spectrometry. It was found to be identical with Manduca AKH. This, together with earlier observations, demonstrates that in M. sexta AKH controls glycogen phosphorylase activation in starving larvae while in adults it controls lipid mobilization during flight. Larval corpora cardiaca contain about 10 times less AKH than the corpora cardiaca of adults. The corpora cardiaca of M. sexta appear to contain only one AKH.

Insect lipid transfer particle catalyzes diacylglycerol exchange between high-density and very-high-density lipoproteins

Facilitated diacylglycerol exchange between Manduca sexta [3H]diacylglycerol-labeled high-density lipophorin and Heliothis zea very-high-density chromolipoprotein was studied. M. sexta lipid transfer particle was employed in assays which measured exchange of [3H]diacylglycerol. Following incubations with lipid transfer particle, donor and acceptor lipoproteins were reisolated by density-gradient ultracentrifugation to determine facilitated exchange. The reaction was limited to diacylglycerol exchange, while donor or acceptor particle apoprotein exchange did not occur. Lipid analysis of donor and acceptor lipoproteins after the lipid-exchange reaction revealed that the labeled diacylglycerol remained unchanged. Lipid transfer particle-catalyzed diacylglycerol exchange was linear up to 0.3 micrograms lipid transfer particle protein in a standard assay and exchange occurred at a rate of 2.5 micrograms diacylglycerol min-1.micrograms-1 lipid transfer particle protein. The assay method was used to show that the hemolymph concentration of lipid transfer particle increased during development.

Bilirubin-binding protein in the serum of spawning-migrating chum salmon,Oncorhynchus keta: Its identity with carotenoid-carrying lipoprotein

The serum carotenoid level gradually increased during the spawning migration of chum salmon (Oncorhynchus keta). Zeaxanthin, a yellowish carotenoid, was detected in the serum of spent males, while astaxanthin was a main carotenoid in the serum of males and females at other developmental stages. A high bilirubin level was found in the serum of spent males; the serum of spent male was yellow in colour due to the presence of zeaxanthin and bilirubin, although the serum of the other fish was bright orange.Three types of carotenoid-carrying lipoprotein such as low density lipoprotein, high density lipoprotein (HDL) and very high density lipoprotein fractions were present in the serum. Carotenoid-carrying lipoprotein from the HDL fraction became a main component during spawning migration. The serum bilirubin from the spent male salmon was distributed in the HDL fraction. Because bilirubin, as well as carotenoids, were present in the HDL fraction, the carotenoid-carrying lipoprotein from the HDL fraction was identical with bilirubin-binding protein in the serum of spent males. This carrier lipoprotein had two subunits (molecular weight 24,000 and 12,000); no disulfide bond was detected between the two subunits.