HeLp, a heme lipoprotein from the hemolymph of the cattle tick, Boophilus microplus

The Pandinus imperator haemolymph lipoprotein, an unusual phosphatidylserine carrying lipoprotein

The haemolymph lipoprotein of the scorpion, Pandinus imperator was isolated and characterised. Contrary to the lipoproteins of insects and the discoidal HDL-lipoproteins of a crayfish and polychaete, the Pandinus lipoprotein consists of three instead of two apoproteins (apoPiLp I = 230 kDa, apoPiLp II = 130 kDa and apoPiLp III = 120 kDa). The apolipoproteins are arranged in varying stoichiometries as judged by cross-linking experiments. In lipoprotein samples from individual animals, the two smaller subunits occurred in a 1:1 stoichiometry, while the relative amount of the 230 kDa peptide varied. The lipoprotein is a slightly heart-shaped HDL with a diameter of approximately 15 nm. It is present in two densities of 1100 and 1190 kg/m(3), of which the latter is by far more abundant. The native molecular mass was estimated to be approximately 500 kDa. The lipid content was determined as 33.5% and consists of approximately 70% neutral lipids and approximately 30% phospholipids. Strikingly, 42.5% of the phospholipids is phosphatidylserine while phosphatidylcholine and phosphatidylethanolamine account for 55.1% and approximately 2.3%, respectively. Carbohydrate analysis suggests the presence of only high-mannose-type N-glycans. N-glycan profiling shows glycans corresponding to a size of 8.0-11.5 hexose units.

Heme-binding storage proteins in the Chelicerata

Lipoglycoproteins in the Chelicerata that bind and store heme appear to represent a unique evolutionary strategy to both mitigate the toxicity of heme and utilize the molecule as a prosthetic group. Knowledge of heme-binding storage proteins in these organisms is in its infancy and much of what is known is from studies with vitellogenins (Vg) and more recently the main hemolymph storage protein in ixodid ticks characterized as a hemelipoglyco-carrier protein (CP). Data have also been reported from another arachnid, the black widow spider, Latrodectus mirabilis, and seem to suggest that the heme-binding capability of these large multimeric proteins is not a phenomenon found only in the Acari. CP appears to be most closely related to Vg in ticks in terms of primary structure but post-translational processing is different. Tick CP and L. mirabilis high-density lipoprotein 1 (HDL1) are similar in that they consist of two subunits of approximate molecular masses of 90 and 100 kDa, are found in the hemolymph as the dominant protein, and bind lipids, carbohydrates and cholesterol. CP binds heme which may also be the case for HDL1 since the protein was found to contain a brown pigment when analyzed by native polyacrylamide gel electrophoresis. Vgs in ticks are composed of multiple subunits and are the precursor of the yolk protein, vitellin. The phylogeny of these proteins, regulation of gene expression and putative functions of binding and storing heme throughout reproduction, blood-feeding and development are discussed. Comparisons with non-chelicerate arthropods are made in order to highlight the mechanisms and putative functions of heme-binding storage proteins and their possible critical function in the evolution of hematophagy.

Knockdown of proteins involved in iron metabolism limits tick reproduction and development

Ticks are among the most important vectors of a wide range of human and animal diseases. During blood feeding, ticks are exposed to an enormous amount of free iron that must be appropriately used and detoxified. However, the mechanism of iron metabolism in ticks is poorly understood. Here, we show that ticks possess a complex system that efficiently utilizes, stores and transports non-heme iron within the tick body. We have characterized a new secreted ferritin (FER2) and an iron regulatory protein (IRP1) from the sheep tick, Ixodes ricinus, and have demonstrated their relationship to a previously described tick intracellular ferritin (FER1). By using RNA interference-mediated gene silencing in the tick, we show that synthesis of FER1, but not of FER2, is subject to IRP1-mediated translational control. Further, we find that depletion of FER2 from the tick plasma leads to a loss of FER1 expression in the salivary glands and ovaries that normally follows blood ingestion. We therefore suggest that secreted FER2 functions as the primary transporter of non-heme iron between the tick gut and the peripheral tissues. Silencing of the fer1, fer2, and irp1 genes by RNAi has an adverse impact on hatching rate and decreases postbloodmeal weight in tick females. Importantly, knockdown of fer2 dramatically impairs the ability of ticks to feed, thus making FER2 a promising candidate for development of an efficient anti-tick vaccine.

Molecular characterization of the major hemelipoglycoprotein in ixodid ticks

The major hemelipoglyco-carrier protein (CP) found throughout the development of male and female adult American dog ticks, Dermacentor variabilis (Say) was sequenced. DvCP is a single transcript coding for two protein subunits that together contain three motifs: (1) a lipoprotein n-terminal domain that is a common attribute of proteins that bind lipids, carbohydrates and metals; (2) a domain of unknown function characteristic of proteins with several large open beta sheets; and (3) a von Willebrand factor type D domain near the carboxy-terminus apparently important for multimerization. These motifs, which are also found in tick vitellogenin, are not shared by heme-binding proteins studied thus far in other hematophagous insects. DvCP message was highest in fat body and salivary gland but was also found in midgut and ovary tissue. Expression was initiated by blood feeding in virgin females and not by mating, as is typical of tick vitellogenin; and the message was found in fed males at levels similar to part fed, virgin females. CP appears to be highly conserved among the Ixodida. The closest match by BlastP to DvCP is vitellogenin from Caenorhabditis elegans (AAC04423), suggesting that CP is a novel protein. The role of CP in heme sequestration, the evolution of hematophagy and host complementation are discussed.

Dynamics of lipid accumulation by the fat body of Rhodnius prolixus: the involvement of lipophorin binding sites

In insects, lipids are stored in the fat body, mainly as triacylglycerol (TAG). In Rhodnius prolixus, a hematophagous hemipteran, lipids are accumulated after blood meal to be used later on. In adult females, at the second day after feeding, the amount of TAG was 57+/-17 microg/fat body, it increased almost five times and at fourth day it was 244+/-35 microg/fat body. TAG content remained constant until day 13, but it then decreased and, at day 20th it was very low (31+/-4.9 microg/fat body). Radiolabeled free fatty acid was used to follow lipid accumulation by the fat body, as it was previously shown that, in R. prolixus, injected free fatty acids associate with lipophorin, a major hemolymphatic lipoprotein. (3)H-palmitic acid was injected into the hemocoel of R. prolixus females. It disappeared from the hemolymph very rapidly, and radioactivity was incorporated by the fat body. Sixty minutes after injection, radioactivity in the fat body was found mainly in TAGs. The capacity of the fat body to incorporate fatty acids from the hemolymph varied according to the days after blood meal, and it was maximal around the fourth day. Lipophorin binding to specific sites in fat body membrane preparations also showed variation at different days. When membranes obtained from insects at the second, fifth and tenth days were compared, binding was highest at fifth day after feeding.

Biglutaminyl-biliverdin IX alpha as a heme degradation product in the dengue fever insect-vector Aedes aegypti

Hemoglobin digestion in the midgut of hematophagous animals results in the release of its prosthetic group, heme, which is a pro-oxidant molecule. Heme enzymatic degradation is a protective mechanism that has been described in several organisms, including plants, bacteria, and mammals. This reaction is catalyzed by heme oxygenase and results in formation of carbon monoxide, ferrous ion, and biliverdin IXalpha. During digestion, a large amount of a green pigment is produced and secreted into the intestinal lumen of Aedes aegypti adult females. In the case of another blood-sucking insect, the kissing-bug Rhodnius prolixus, we have recently shown that heme degradation involves a complex pathway that generates dicysteinyl-biliverdin IX gamma. The light absorption spectrum of the Aedes purified pigment was similar to that of biliverdin, but its mobility on a reverse-phase chromatography column suggested a compound less hydrophobic than biliverdin IXalpha. Structural characterization by ESI-MS revealed that the mosquito pigment is the alpha isomer of biliverdin bound to two glutamine residues by an amide bond. This biglutaminyl-biliverdin is formed by oxidative cleavage of the heme porphyrin ring followed by two subsequent additions of glutamine residues to the biliverdin IXalpha. The role of this pathway in the adaptation of this insect vector to a blood-feeding habit is discussed.

Extracellular lipid droplets promote hemozoin crystallization in the gut of the blood flukeSchistosoma mansoni

Hemozoin (Hz) is a heme crystal produced upon hemoglobin digestion as the main mechanism of heme disposal in several hematophagous organisms. Here, we show that, in the helminth Schistosoma mansoni, Hz formation occurs in extracellular lipid droplets (LDs). Transmission electron microscopy of adult worms revealed the presence of numerous electron-lucent round structures similar to LDs in gut lumen, where multicrystalline Hz assemblies were found associated to their surfaces. Female regurgitates promoted Hz formation in vitro in reactions partially inhibited by boiling. Fractionation of regurgitates showed that Hz crystallization activity was essentially concentrated on lower density fractions, which have small amounts of pre-formed Hz crystals, suggesting that hydrophilic-hydrophobic interfaces, and not Hz itself, play a key catalytic role in Hz formation in S. mansoni. Thus, these data demonstrate that LDs present in the gut lumen of S. mansoni support Hz formation possibly by allowing association of heme to the lipid-water interface of these structures.

Oxidative stress impairs heme detoxification in the midgut of the cattle tick, Rhipicephalus (Boophilus) microplus

In the cattle tick Rhipicephalus (Boophilus) microplus digestion of blood is intracellular, accomplished by the so-called digest cells that fill the midgut lumen. Hydrolysis of hemoglobin in the digestive vesicles of these cells results in the release of large amounts of heme, a pro-oxidant compound, whose iron atom, together with H(2)O(2), may participate in the Fenton reaction and lead to the production of hydroxyl radicals. Here, we investigated the role of catalase, an enzyme responsible for H(2)O(2) detoxification. Fully engorged female ticks injected with 3-amino-1,2,4-triazole (AT), a catalase inhibitor, showed increased H(2)O(2) in the gut, together with diminished life span and lower egg-laying rates. Increased mortality observed upon AT injection was reversed by further injection of exogenous catalase, 2 days after AT treatment, confirming that increased death was due to inhibition of this enzyme by AT. In primary cultures of digest cells, intracellular H(2)O(2) is limited to specific organelles, while treatment with AT in vitro resulted in increased H(2)O(2) spreading all over the cell, confirming the role of catalase in regulating H(2)O(2) levels. Ticks fed on a calf that had been injected with AT showed marked inhibition of catalase activity in the gut and diminished life span, oviposition and engorgement. Digest cells of these ticks had an altered morphology, showing heme spread all over the cytosol, instead of being limited to the hemosomes. The amount of aggregated heme found in isolated hemosome was also strongly decreased in AT-treated cattle. All together, our results indicate that catalase performs an important role in the control of redox balance in R. microplus, which dramatically affects hemosome formation and stability. This enzyme may be a target in the development of new methods for tick control.

Tracing heme in a living cell: hemoglobin degradation and heme traffic in digest cells of the cattle tick Boophilus microplus

Heme is present in all cells, acting as a cofactor in essential metabolic pathways such as respiration and photosynthesis. Moreover, both heme and its degradation products, CO, iron and biliverdin, have been ascribed important signaling roles. However, limited knowledge is available on the intracellular pathways involved in the flux of heme between different cell compartments. The cattle tick Boophilus microplus ingests 100 times its own mass in blood. The digest cells of the midgut endocytose blood components and huge amounts of heme are released during hemoglobin digestion. Most of this heme is detoxified by accumulation into a specialized organelle, the hemosome. We followed the fate of hemoglobin and albumin in primary cultures of digest cells by incubation with hemoglobin and albumin labeled with rhodamine. Uptake of hemoglobin by digest cells was inhibited by unlabeled globin, suggesting the presence of receptor-mediated endocytosis. After endocytosis, hemoglobin was observed inside large digestive vesicles. Albumin was exclusively associated with a population of small acidic vesicles, and an excess of unlabeled albumin did not inhibit its uptake. The intracellular pathway of the heme moiety of hemoglobin was specifically monitored using Palladium-mesoporphyrin IX (Pd-mP) as a fluorescent heme analog. When pulse and chase experiments were performed using digest cells incubated with Pd-mP bound to globin (Pd-mP-globin), strong yellow fluorescence was found in large digestive vesicles 4 h after the pulse. By 8 h, the emission of Pd-mP was red-shifted and more evident in the cytoplasm, and at 12 h most of the fluorescence was concentrated inside the hemosomes and had turned green. After 48 h, the Pd-mP signal was exclusively found in hemosomes. In methanol, Pd-mP showed maximal emission at 550 nm, exhibiting a red-shift to 665 nm when bound to proteins in vitro. The red emission in the cytosol and at the boundary of hemosomes suggests the presence of heme-binding proteins, probably involved in transport of heme to the hemosome. The existence of an intracellular heme shuttle from the digestive vesicle to the hemosome acting as a detoxification mechanism should be regarded as a major adaptation of ticks to a blood-feeding way of life. To our knowledge, this is the first direct observation of intracellular transport of heme in a living eukaryotic cell. A similar approach, using Pd-mP fluorescence, could be applied to study heme intracellular metabolism in other cell types.

Structural and morphological characterization of hemozoin produced by Schistosoma mansoni and Rhodnius prolixus

Hemozoin (Hz) is a heme crystal produced upon the digestion of hemoglobin (Hb) by blood-feeding organisms as a main mechanism of heme disposal. The structure of Hz consists of heme dimers bound by reciprocal iron-carboxylate interactions and stabilized by hydrogen bonds. We have recently described heme crystals in the blood fluke, Schistosoma mansoni, and in the kissing bug, Rhodnius prolixus. Here, we characterized the structures and morphologies of the heme crystals from those two organisms and compared them to synthetic beta-hematin (betaH). Synchrotron radiation X-ray powder diffraction showed that all heme crystals share the same unit cell and structure. The heme crystals isolated from S. mansoni and R. prolixus consisted of very regular units assembled in multicrystalline spherical structures exhibiting remarkably distinct surface morphologies compared to betaH. In both organisms, Hz formation occurs inside lipid droplet-like particles or in close association to phospholipid membranes. These results show, for the first time, the structural and morphological characterization of natural Hz samples obtained from these two blood-feeding organisms. Moreover, Hz formation occurring in close association to a hydrophobic environment seems to be a common trend for these organisms and may be crucial to produce very regular shaped phases, allowing the formation of multicrystalline assemblies in the guts of S. mansoni and R. prolixus.

Genes transcribed in the salivary glands of female Rhipicephalus appendiculatus ticks infected with Theileria parva

We describe the generation of an auto-annotated index of genes that are expressed in the salivary glands of four-day fed female adult Rhipicephalus appendiculatus ticks. A total of 9162 EST sequences were derived from an uninfected tick cDNA library and 9844 ESTs were from a cDNA library from ticks infected with Theileria parva, which develop in type III salivary gland acini. There were no major differences between abundantly expressed ESTs from the two cDNA libraries, although there was evidence for an up-regulation in the expression of some glycine-rich proteins in infected salivary glands. Gene ontology terms were also assigned to sequences in the index and those with potential enzyme function were linked to the Kyoto encyclopedia of genes and genomes database, allowing reconstruction of metabolic pathways. Several genes code for previously characterized tick proteins such as receptors for myokinin or ecdysteroid and an immunosuppressive protein. cDNAs coding for homologs of heme-lipoproteins which are major components of tick hemolymph were identified by searching the database with published N-terminal peptide sequence data derived from biochemically purified Boophilus microplus proteins. The EST data will be a useful resource for construction of microarrays to probe vector biology, vector-host and vector-pathogen interactions and to underpin gene identification via proteomics approaches.

HeLp, a heme-transporting lipoprotein with an antioxidant role

Plasma lipoproteins involved in lipid transport are target for free radical-evoked pathological conditions in several mammalian models. The main hemolymphatic protein of Boophilus microplus is a heme-binding lipoprotein (HeLp, for Heme LipoProtein) that carries dietary heme produced from degradation of vertebrate hemoglobin to tissues of the tick. Addition of heme to phospholipid liposomes resulted in intense lipid peroxidation, which was inhibited by addition of HeLp. HeLp prevented lysis of red blood cells by heme. HeLp also inhibited reactions of heme with tert-butyl hydroperoxide (t-BOOH) or hydrogen peroxide. HeLp, quite differently from other lipoproteins, presents a protective intrinsic mechanism to counteract heme toxicity, while preserving the heme molecule to be reused by the tick. This is the first report of a lipoprotein acting as an antioxidant particle against heme-induced radical damage.

A new intracellular pathway of haem detoxification in the midgut of the cattle tick Boophilus microplus: aggregation inside a specialized organelle, the hemosome

The hard tick Boophilus microplus ingests large volumes of cattle blood, as much as 100 times its own mass before feeding. Huge amounts of haem are produced during haemoglobin digestion, which takes place inside acidic lysosomal-type vacuoles of the digest cells of the midgut. Haem is a promoter of free radical formation, so haemoglobin digestion poses an intense oxidative challenge to this animal. In the present study we followed the fate of the haem derived from haemoglobin hydrolysis in the digest cells of the midgut of fully engorged tick females. The tick does not synthesize haem, so during the initial phase of blood digestion, absorption is the major route taken by the haem, which is transferred from the digest cells to the tick haemocoel. After this absorptive period of a few days, most of the haem produced upon haemoglobin degradation is accumulated in the interior of a specialized, membrane-delimited, organelle of the digest cell, herein called hemosome. Haem accounts for 90% of the hemosome mass and is concentrated in the core of this structure, appearing as a compact, non-crystalline aggregate of iron protoporphyrin IX without covalent modifications. The unusual FTIR spectrum of this aggregate suggests that lateral propionate chains are involved in the association of haem molecules with other components of the hemosome, which it is proposed is a major haem detoxification mechanism in this blood-sucking arthropod.

Molecular cloning, expression and isolation of ferritins from two tick species--Ornithodoros moubata and Ixodes ricinus

Genes encoding ferritins were isolated and cloned from cDNA libraries of hard tick Ixodes ricinus and soft tick Ornithodoros moubata. Both tick ferritins are composed of 172 amino-acid residues and their calculated mass is 19,667.2 Da and 19,974.5 Da for I. ricinus and O. moubata, respectively. The sequences of both proteins are closely related to each other as well as to the ferritin from another tick species Dermacentor variabilis (>84% similarity). The proteins contain the conserved motifs for ferroxidase center typical for heavy chains of vertebrate ferritins. The stem-loop structure of a putative iron responsive element was found in the 5' untranslated region of ferritin mRNA of both ticks. Antibodies against fusion ferritin from O. moubata were raised in a rabbit and used to monitor the purification of a small amount of ferritins from both tick species. The authenticity of ferritin purified from O. moubata was confirmed by mass-fingerprinting analysis. In the native state, the tick ferritins are apparently larger (~500 kDa) than horse spleen ferritin (440 kDa). On SDS-PAGE tick ferritins migrate as a single band of about 21 kDa. These results suggest that tick ferritins are homo-oligomers of 24 identical subunits of heavy-chain type. The Northern blot analysis revealed that O. moubata ferritin mRNA level is likely not up-regulated after ingestion of a blood meal.

Binding and storage of heme by vitellin from the cattle tick, Boophilus microplus

We have previously shown (, Curr. Biol. 9, 703-706) that the cattle tick Boophilus microplus does not synthesize heme, relying solely on the recovery of the heme from the diet to make all its hemeproteins. Here we present evidence that Vitellin (VN(1)), the main tick yolk protein, is a reservoir of heme for embryo development. VN was isolated from eggs at different days throughout embryogenesis. Immediately after oviposition, Boophilus VN contains approximately one mol of heme/mol of protein. During embryo development about one third of egg VN is degraded. The remaining VN molecules bind part of the heme released. These results suggest that VN functions as a heme reservoir, binding any free heme that exceeds the amount needed for development. In vitro measurement of the binding of heme to VN showed that each VN molecule binds up to 31 heme molecules. The association of heme with VN strongly inhibits heme-induced lipid peroxidation, suggesting that binding of heme is an important antioxidant mechanism to protect embryo cells from oxidative damage. This mechanism allows this hematophagous arthropod to safely store heme obtained from a blood meal inside their eggs for future use. Taken together our data suggest that, besides its known roles, VN also plays additional functions as a heme deposit and an antioxidant protective molecule.

Hemolymph proteins in ticks

In comparison to insects and Crustacea, our knowledge of the predominant hemolymph proteins in ticks is minimal. The hemolymph protein most studied in ticks has been vitellogenin (Vg). Vg is synthesized by the tick fat body after female adults obtain a blood meal, is released into the hemolymph and is absorbed by developing oocytes as vitellin (Vn). Much of what we know about Vg is from studies of Vn. In general, the carbohydrate, lipid and amino acid composition is similar to insects except that in the tick, Vg contains heme, most likely from the digestion of host hemoglobin. In the American dog tick, Dermacentor variabilis, Vg is comprised of two native proteins and seven subunits on SDS-PAGE. Vg has been characterized in five tick species but the amino acid sequence is not yet available. Another predominant hemolymph protein, apparently a carrier protein (CP), has recently been studied in two tick species. This protein is found in the hemolymph of both male and females adults, in adult tissues outside of the hemolymph in some tick species, in coxal fluid of soft ticks and in whole body homogenates from eggs, larvae and nymphs. CP from the hard tick, D. variabilis, contains cholesterol, phospholipids, monoacylglycerides, triacylglycerides, free fatty acids, carbohydrate and heme. Under identical assay conditions, the analogous protein in the soft tick, Ornithodoros parkeri, did not contain heme. CP in the American dog tick consists of two subunits, one of which has 61% identity to the biliprotein, artemocyanin, from the fairy shrimp. CP is identical to a heme-lipoprotein (HeLp) from Boophilus microplus. The exact roles of CP and HeLp have not yet been fully determined, but they apparently are important in heme sequestration and as a storage depot for protein and lipid. Macroglobulin, lectin, antimicrobial, JH binding, JH esterase, and other tick hemolymph proteins are also discussed.

Tissue distribution and characterization of predominant hemolymph carrier proteins from Dermacentor variabilis and Ornithodoros parkeri

The tissue distribution of the predominant hemolymph protein found throughout tick development was examined in the hard tick, Dermacentor variabilis, and in the soft tick, Ornithodoros parkeri. In D. variabilis, the predominant (purified) hemolymph protein was a lipoglycoheme-carrier protein (DvCP) with a molecular weight of 200K. A protein with a similar mobility on native-PAGE was found in fat body, salivary gland, muscle and ovary from partially fed females which was most abundant in the plasma and salivary gland. DvCP from plasma, salivary gland and fat body of partially fed females consisted of two subunits on SDS-PAGE (98 and 92K). In replete females, only salivary gland exhibited protein subunits equivalent to hemolymph CP. CP in salivary gland and fat body stained positive for lipids. The concentration of CP in tissues varied between partially fed and replete females, indicating a difference in the expression and/or sequestration of CP during adult development. The predominant hemolymph carrier protein from O. parkeri (OpCP) was purified to homogeneity for the first time and is presumed to have similar functions to CP from D. variabilis. Purified OpCP exhibited a molecular weight of 668K by native-PAGE. Unlike CP from D. variabilis, OpCP was not detected in fat body or salivary gland tissues but occurred abundantly in coxal fluid. By SDS-PAGE, purified hemolymph OpCP consisted of two major subunits (114 and 93K) and a less abundant protein with an apparent molecular weight of 48K. Purified native OpCP was a lipoprotein like DvCP. A spectral analysis of purified OpCP failed to demonstrate the presence of heme like that found for CP from D. variabilis, purified by the same methods. However, plasma from O. parkeri contained heme with a lambda(max) of 410nm.

Reduced oviposition of Boophilus microplus feeding on sheep vaccinated with vitellin

The most abundant protein present in Boophilus microplus eggs, vitellin, was isolated and purified as a non-covalent complex of six glyco-polypeptides of Mr 44-107kDa. The protein complex bound haem. Immuno-blots demonstrated that antibodies raised to vitellin recognised a 200kDa polypeptide in the haemolymph of adult female ticks. This is consistent with the general proposal that in arthropods vitellin is derived by proteolytic processing from a large precursor protein, vitellogenin. In parallel with this study, an 80kDa glycoprotein (GP80) was independently purified from larvae of B. microplus using efficacy in vaccination trials as an assay. Antibodies to GP80 also recognised a 200kDa protein in the haemolymph of ticks and a major 87kDa polypeptide present in the vitellin complex. Conversely, antibodies to purified vitellin recognised GP80. The amino-terminal amino acid sequences of the 87kDa vitellin polypeptide and GP80 were identical for at least the first 11 residues and internal peptide sequences from both polypeptides were co-located in a single but incomplete deduced amino sequence of B. microplus vitellogenin. Thus, GP80 is a processed product from vitellogenin and highly related to but not completely identical with the 87kDa vitellin polypeptide. Vaccination trials in the model host sheep were performed with purified vitellin and GP80. Sheep vaccinated with either purified vitellin or GP80 returned significantly reduced numbers of engorged female ticks with decreased weights and reduced oviposition. In contrast, sheep vaccinated with recombinant hexahis-GP80, which was incorrectly folded and not glycosylated showed no significant effects on ticks. It was concluded that vitellin and GP80 could induce immune responses that partially protect sheep from the tick, B. microplus. However, critical protective epitopes are associated with the folding of the protein and/or the oligosaccharides attached to it.

Serine proteinase inhibitors from eggs and larvae of tick Boophilus microplus: purification and biochemical characterization

The present study describes the purification, characterization, and comparison of serine proteinase inhibitors during the development of egg and larva phases of the tick Boophilus microplus. Samples were collected of eggs between the first day of hatching and the beginning of eclosion (defined as El, E2, and E3) and of larvae between the first day of eclosion and the infectant phase (defined as L1, L2, and L3). Crude extracts of the samples (2.5% w/v in Tris-HCI buffer) were analyzed by SDS-PAGE, and showed three major protein bands of 42, 62, and 85 kDa, differing in intensity, from E1 to L3 samples. The total protein of the larva extracts was 34% less than that of the egg extracts, while no differences in active protein were detected. The apparent dissociation constant Ki determined for trypsin was 10-fold lower from E1 to L3 samples. Serine proteinase inhibitors from tick eggs and larvae (BmTls) were purified on trypsin-Sepharose column and analyzed by SDS-PAGE. The results showed a slight difference in protein pattern, with a protein band of 20 kDa in the E1 and E2 samples which did not appear in the other samples. The Ki for neutrophil elastase was 10-fold lower in L3 than E1. BmTI reverse-phase chromatography showed two and one major peaks in egg and larva samples, respectively. The N-terminal amino acid sequence of the L3 main peak from a C8 column showed a mix of BmTIs with the major sequence AVDFDKGCVPTADPGPCKG. Changes indicated by molecular weight and inhibition activity suggest different roles for BmTIs during the development process.