The major tick salivary gland proteins and toxins from the soft tick, Ornithodoros savignyi, are part of the tick Lipocalin family: implications for the origins of tick toxicoses

The venom and telopodal defence systems of the centipede Lithobius forficatus are functionally convergent serial homologues

BACKGROUND

Evolution of novelty is a central theme in evolutionary biology, yet studying the origins of traits with an apparently discontinuous origin remains a major challenge. Venom systems are a well-suited model for the study of this phenomenon because they capture several aspects of novelty across multiple levels of biological complexity. However, while there is some knowledge on the evolution of individual toxins, not much is known about the evolution of venom systems as a whole. One way of shedding light on the evolution of new traits is to investigate less specialised serial homologues, i.e. repeated traits in an organism that share a developmental origin. This approach can be particularly informative in animals with repetitive body segments, such as centipedes.

RESULTS

Here, we investigate morphological and biochemical aspects of the defensive telopodal glandular organs borne on the posterior legs of venomous stone centipedes (Lithobiomorpha), using a multimethod approach, including behavioural observations, comparative morphology, proteomics, comparative transcriptomics and molecular phylogenetics. We show that the anterior venom system and posterior telopodal defence system are functionally convergent serial homologues, where one (telopodal defence) represents a model for the putative early evolutionary state of the other (venom). Venom glands and telopodal glandular organs appear to have evolved from the same type of epidermal gland (four-cell recto-canal type) and while the telopodal defensive secretion shares a great degree of compositional overlap with centipede venoms in general, these similarities arose predominantly through convergent recruitment of distantly related toxin-like components. Both systems are composed of elements predisposed to functional innovation across levels of biological complexity that range from proteins to glands, demonstrating clear parallels between molecular and morphological traits in the properties that facilitate the evolution of novelty.

CONCLUSIONS

The evolution of the lithobiomorph telopodal defence system provides indirect empirical support for the plausibility of the hypothesised evolutionary origin of the centipede venom system, which occurred through functional innovation and gradual specialisation of existing epidermal glands. Our results thus exemplify how continuous transformation and functional innovation can drive the apparent discontinuous emergence of novelties on higher levels of biological complexity.

Saliva proteome of partially- and fully-engorged adult female Haemaphysalis flava ticks

Tick saliva is a reservoir of bioactive proteins. Saliva protein compositions change dynamically during blood-feeding. Decipherment of protein profiles in different blood-feeding stages may bring deeper insight into tick feeding physiology and provide targets for immunologic control alternatives. However, having the infancy of tick genome sequencing, assembly, annotation, and limited knowledge of tick salivary proteins restrain the data interpretation. Here, we aimed to depict the saliva protein profile in partially- (PE) and fully-engorged (FE) Haemaphysalis flava ticks, with a special focus on the analysis of those uncharacterized proteins. Saliva was collected from PE and FE adult female H. flava ticks. Saliva proteins were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS-MS). MS data were searched against an in-house salivary gland transcriptome library for identification of tick-derived proteins. Abundances of proteins were compared between PE and FE ticks. The uncharacterized proteins detected in saliva were further bioinformatically analyzed. In total, 614 proteins were identified including 94 host proteins and 520 tick-derived proteins. The 226 tick-derived high-confidence proteins were classified into 10 categories: transporters, enzymes, protease inhibitors, immunity-related proteins, lipocalins, glycine-rich proteins, muscle proteins, secreted proteins, uncharacterized proteins and others. A total of 98 proteins were shared in both PE and FE with 74 only in PE and 54 only in FE. Abundances of 24 shared proteins were significantly higher in PE. The profile of top 15 most abundant proteins was also different between PE and FE ticks. The 65 uncharacterized proteins detected in tick saliva were branched into subclusters 1 A, 1B, 2, 3 A, 3B and 3 C based on particular motifs like RGD, LRR, indicating their diverse predicted functions like anti-coagulation, regulation of innate immune, or other functions. This study provides and compares saliva proteomes of H. flava ticks in two feeding stages with special cluster analysis on the uncharacterized proteins. Further investigations are needed to confirm the roles of these uncharacterized proteins in ticks.

Mass spectrometry analysis of human tear fluid biomarkers specific for ocular and systemic diseases in the context of 3P medicine

Over the last two decades, a large number of non-communicable/chronic disorders reached an epidemic level on a global scale such as diabetes mellitus type 2, cardio-vascular disease, several types of malignancies, neurological and eye pathologies-all exerted system's enormous socio-economic burden to primary, secondary, and tertiary healthcare. The paradigm change from reactive to predictive, preventive, and personalized medicine (3PM/PPPM) has been declared as an essential transformation of the overall healthcare approach to benefit the patient and society at large. To this end, specific biomarker panels are instrumental for a cost-effective predictive approach of individualized prevention and treatments tailored to the person. The source of biomarkers is crucial for specificity and reliability of diagnostic tests and treatment targets. Furthermore, any diagnostic approach preferentially should be noninvasive to increase availability of the biomaterial, and to decrease risks of potential complications as well as concomitant costs. These requirements are clearly fulfilled by tear fluid, which represents a precious source of biomarker panels. The well-justified principle of a "sick eye in a sick body" makes comprehensive tear fluid biomarker profiling highly relevant not only for diagnostics of eye pathologies but also for prediction, prognosis, and treatment monitoring of systemic diseases. One prominent example is the Sicca syndrome linked to a cascade of severe complications that include dry eye, neurologic, and oncologic diseases. In this review, protein profiles in tear fluid are highlighted and corresponding biomarkers are exemplified for several relevant pathologies, including dry eye disease, diabetic retinopathy, cancers, and neurological disorders. Corresponding analytical approaches such as sample pre-processing, differential proteomics, electrophoretic techniques, high-performance liquid chromatography (HPLC), enzyme-linked immuno-sorbent assay (ELISA), microarrays, and mass spectrometry (MS) methodology are detailed. Consequently, we proposed the overall strategies based on the tear fluid biomarkers application for 3P medicine practice. In the context of 3P medicine, tear fluid analytical pathways are considered to predict disease development, to target preventive measures, and to create treatment algorithms tailored to individual patient profiles.

Immunomodulatory Proteins in Tick Saliva From a Structural Perspective

To feed successfully, ticks must bypass or suppress the host’s defense mechanisms, particularly the immune system. To accomplish this, ticks secrete specialized immunomodulatory proteins into their saliva, just like many other blood-sucking parasites. However, the strategy of ticks is rather unique compared to their counterparts. Ticks’ tendency for gene duplication has led to a diverse arsenal of dozens of closely related proteins from several classes to modulate the immune system’s response. Among these are chemokine-binding proteins, complement pathways inhibitors, ion channels modulators, and numerous poorly characterized proteins whose functions are yet to be uncovered. Studying tick immunomodulatory proteins would not only help to elucidate tick-host relationships but would also provide a rich pool of potential candidates for the development of immunomodulatory intervention drugs and potentially new vaccines. In the present review, we will attempt to summarize novel findings on the salivary immunomodulatory proteins of ticks, focusing on biomolecular targets, structure-activity relationships, and the perspective of their development into therapeutics.

Diet Diversity in Carnivorous Terebrid Snails Is Tied to the Presence and Absence of a Venom Gland

Predator-prey interactions are thought to play a driving role in animal evolution, especially for groups that have developed venom as their predatory strategy. However, how the diet of venomous animals influences the composition of venom arsenals remains uncertain. Two prevailing hypotheses to explain the relationship between diet and venom composition focus on prey preference and the types of compounds in venom, and a positive correlation between dietary breadth and the number of compounds in venom. Here, we examined venom complexity, phylogenetic relationship, collection depth, and biogeography of the Terebridae (auger snails) to determine if repeated innovations in terebrid foregut anatomy and venom composition correspond to diet variation. We performed the first molecular study of the diet of terebrid marine snails by metabarcoding the gut content of 71 terebrid specimens from 17 species. Our results suggest that the presence or absence of a venom gland is strongly correlated with dietary breadth. Specifically, terebrid species without a venom gland displayed greater diversity in their diet. Additionally, we propose a revision of the definition of venom complexity in conoidean snails to more accurately capture the breadth of ecological influences. These findings suggest that prey diet is an important factor in terebrid venom evolution and diversification and further investigations of other understudied organisms, like terebrids, are needed to develop robust hypotheses in this area.

Quantitative Visions of Reality at the Tick-Host Interface: Biochemistry, Genomics, Proteomics, and Transcriptomics as Measures of Complete Inventories of the Tick Sialoverse

Species have definitive genomes. Even so, the transcriptional and translational products of the genome are dynamic and subject to change over time. This is especially true for the proteins secreted by ticks at the tick-host feeding interface that represent a complex system known as the sialoverse. The sialoverse represent all of the proteins derived from tick salivary glands for all tick species that may be involved in tick-host interaction and the modulation of the host's defense mechanisms. The current study contemplates the advances made over time to understand and describe the complexity present in the sialoverse. Technological advances at given periods in time allowed detection of functions, genes, and proteins enabling a deeper insight into the complexity of the sialoverse and a concomitant expansion in complexity with as yet, no end in sight. The importance of systematic classification of the sialoverse is highlighted with the realization that our coverage of transcriptome and proteome space remains incomplete, but that complete descriptions may be possible in the future. Even so, analysis and integration of the sialoverse into a comprehensive understanding of tick-host interactions may require further technological advances given the high level of expected complexity that remains to be uncovered.

Integrated analysis of sialotranscriptome and sialoproteome of the brown dog tick Rhipicephalus sanguineus (s.l.): Insights into gene expression during blood feeding

Tick salivary glands secrete a complex saliva into their hosts which modulates vertebrate hemostasis, immunity and tissue repair mechanisms. Transcriptomic studies revealed a large number of transcripts coding for structural and secreted protein products in a single tick species. These transcripts are organized in several large families according to their products. Not all transcripts are expressed at the same time, transcription profile switches at intervals, characterizing the phenomenon of "sialome switching". In this work, using transcriptomic and proteomic analysis we explored the sialome of Rhipicephalus sanguineus (s.l.) adult female ticks feeding on a rabbit. The correlations between transcriptional and translational results in the different groups were evaluated, confirming the "sialome switching" and validating the idea that the expression switch may serve as a mechanism of escape from the host immunity. Recombination breakpoints were identified in lipocalin and metalloprotease families, indicating this mechanism could be a possible source of diversity in the tick sialome. Another remarkable observation was the identification of host-derived proteins as a component of tick salivary gland content. These results and disclosed sequences contribute to our understanding of tick feeding biology, to the development of novel anti-tick methods, and to the discovery of novel pharmacologically active products. SIGNIFICANCE: Ticks are a burden by themselves to humans and animals, and vectors of viral, bacterial, protozoal and helminthic diseases. Their saliva has anti-clotting, anti-platelet, vasodilatory and immunomodulatory activities that allows successful feeding and pathogen transmission. Previous transcriptomic studies indicate ticks to have over one thousand transcripts coding for secreted salivary proteins. These transcripts code for proteins of diverse families, but not all are transcribed simultaneously, but rather transiently, in a succession. Here we explored the salivary transcriptome and proteome of the brown dog tick, Rhipicephalus sanguineus. A protein database of over 20 thousand sequences was "de novo" assembled from over 600 million nucleotide reads, from where over two thousand polypeptides were identified by mass spectrometry. The proteomic data was shown to vary in time with the transcription profiles, validating the idea that the expression switch may serve as a mechanism of escape from the host immunity. Analysis of the transcripts coding for lipocalin and metalloproteases indicate their genes to contain signals of breakpoint recombination suggesting a new mechanism responsible for the large diversity in tick salivary proteins. These results and the disclosed sequences contribute to our understanding of the success ticks enjoy as ectoparasites, to the development of novel anti-tick methods, and to the discovery of novel pharmacologically active products.

Tick-Borne Encephalitis Virus Infection Alters the Sialome of Ixodes ricinus Ticks During the Earliest Stages of Feeding

Ticks are hematophagous arthropods that transmit a number of pathogens while feeding. Among these is tick-borne encephalitis virus (TBEV), a flavivirus transmitted by Ixodes ricinus ticks in the temperate zone of Europe. The infection results in febrile illness progressing to encephalitis and meningitis with a possibility of fatality or long-term neurological sequelae. The composition of tick saliva plays an essential role in the initial virus transmission during tick feeding. Ticks secrete a diverse range of salivary proteins to modulate the host response, such as lipocalins to control the itch and inflammatory response, and both proteases and protease inhibitors to prevent blood coagulation. Here, the effect of viral infection of adult females of Ixodes ricinus was studied with the goal of determining how the virus alters the tick sialome to modulate host tissue response at the site of infection. Uninfected ticks or those infected with TBEV were fed on mice and removed and dissected one- and 3-h post-attachment. RNA from the salivary glands of these ticks, as well as from unfed ticks, was extracted and subjected to next-generation sequencing to determine the expression of key secreted proteins at each timepoint. Genes showing statistically significant up- or down-regulation between infected and control ticks were selected and compared to published literature to ascertain their function. From this, the effect of tick viral infection on the modulation of the tick-host interface was determined. Infected ticks were found to differentially express a number of uncategorized genes, proteases, Kunitz-type serine protease inhibitors, cytotoxins, and lipocalins at different timepoints. These virus-induced changes to the tick sialome may play a significant role in facilitating virus transmission during the early stages of tick feeding.

Differential Tick Salivary Protein Profiles and Human Immune Responses to Lone Star Ticks (Amblyomma americanum) From the Wild vs. a Laboratory Colony

Ticks are a growing concern to human and animal health worldwide and they are leading vectors of arthropod-borne pathogens in the United States. Ticks are pool blood feeders that can attach to the host skin for days to weeks using their saliva to counteract the host defenses. Tick saliva, as in other hematophagous arthropods, contains pharmacological and immunological active compounds, which modulate local and systemic immune responses and induce antibody production. In the present study, we explore differences in the salivary gland extract (SGE) protein content of Amblyomma americanum ticks raised in a laboratory colony (CT) vs. those collected in the field (FT). First, we measured the IgG antibody levels against SGE in healthy volunteers residing in Kansas. ELISA test showed higher IgG antibody levels when using the SGE from CT as antigen. Interestingly, antibody levels against both, CT-SGE and FT-SGE, were high in the warm months (May-June) and decreased in the cold months (September-November). Immunoblot testing revealed a set of different immunogenic bands for each group of ticks and mass spectrometry data revealed differences in at 19 proteins specifically identified in the CT-SGE group and 20 from the FT-SGE group. Our results suggest that differences in the salivary proteins between CT-SGE and FT-SGE may explain the differential immune responses observed in this study.

Deciphering Biological Processes at the Tick-Host Interface Opens New Strategies for Treatment of Human Diseases

Ticks are obligatory blood-feeding ectoparasites, causing blood loss and skin damage in their hosts. In addition, ticks also transmit a number of various pathogenic microorganisms that cause serious diseases in humans and animals. Ticks evolved a wide array of salivary bioactive compounds that, upon injection into the host skin, inhibit or modulate host reactions such as hemostasis, inflammation and wound healing. Modulation of the tick attachment site in the host skin involves mainly molecules which affect physiological processes orchestrated by cytokines, chemokines and growth factors. Suppressing host defense reactions is crucial for tick survival and reproduction. Furthermore, pharmacologically active compounds in tick saliva have a promising therapeutic potential for treatment of some human diseases connected with disorders in hemostasis and immune system. These disorders are often associated to alterations in signaling pathways and dysregulation or overexpression of specific cytokines which, in turn, affect mechanisms of angiogenesis, cell motility and cytoskeletal regulation. Moreover, tick salivary molecules were found to exert cytotoxic and cytolytic effects on various tumor cells and have anti-angiogenic properties. Elucidation of the mode of action of tick bioactive molecules on the regulation of cell processes in their mammalian hosts could provide new tools for understanding the complex changes leading to immune disorders and cancer. Tick bioactive molecules may also be exploited as new pharmacological inhibitors of the signaling pathways of cytokines and thus help alleviate patient discomfort and increase patient survival. We review the current knowledge about tick salivary peptides and proteins that have been identified and functionally characterized in in vitro and/or in vivo models and their therapeutic perspective.

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Argasid and ixodid systematics: Implications for soft tick evolution and systematics, with a new argasid species list

The systematics of the genera and subgenera within the soft tick family Argasidae is not adequately resolved. Different classification schemes, reflecting diverse schools of scientific thought that elevated or downgraded groups to genera or subgenera, have been proposed. In the most recent classification scheme, Argas and Ornithodoros are paraphyletic and the placement of various subgenera remains uncertain because molecular data are lacking. Thus, reclassification of the Argasidae is required. This will enable an understanding of soft tick systematics within an evolutionary context. This study addressed that knowledge gap using mitochondrial genome and nuclear (18S and 28S ribosomal RNA) sequence data for representatives of the subgenera Alectorobius, Argas, Chiropterargas, Ogadenus, Ornamentum, Ornithodoros, Navis (subgen. nov.), Pavlovskyella, Persicargas, Proknekalia, Reticulinasus and Secretargas, from the Afrotropical, Nearctic and Palearctic regions. Hard tick species (Ixodidae) and a new representative of Nuttalliella namaqua (Nuttalliellidae), were also sequenced with a total of 83 whole mitochondrial genomes, 18S rRNA and 28S rRNA genes generated. The study confirmed the utility of next-generation sequencing to retrieve systematic markers. Paraphyly of Argas and Ornithodoros was resolved by systematic analysis and a new species list is proposed. This corresponds broadly with the morphological cladistic analysis of Klompen and Oliver (1993). Estimation of divergence times using molecular dating allowed dissection of phylogeographic patterns for argasid evolution. The discovery of cryptic species in the subgenera Chiropterargas, Ogadenus and Ornithodoros, suggests that cryptic speciation is common within the Argasidae. Cryptic speciation has implications for past biological studies of soft ticks. These are discussed in particular for the Ornithodoros (Ornithodoros) moubata and Ornithodoros (Ornithodoros) savignyi groups.

Tick Paralysis: Solving an Enigma

In comparison to other arachnids, ticks are major vectors of disease, but less than 8% of the known species are capable of inducing paralysis, as compared to the ~99⁻100% arachnids that belong to venomous classes. When considering the potential monophyly of venomous Arachnida, this review reflects on the implications regarding the classification of ticks as venomous animals and the possible origin of toxins. The origin of tick toxins is compared with scorpion and spider toxins and venoms based on their significance, functionality, and structure in the search to find homologous venomous characters. Phenotypic evaluation of paralysis, as caused by different ticks, demonstrated the need for expansion on existing molecular data of pure isolated tick toxins because of differences and discrepancies in available data. The use of in-vivo, in-vitro, and in-silico assays for the purification and characterization of paralysis toxins were critically considered, in view of what may be considered to be a paralysis toxin. Purified toxins should exhibit physiologically relevant activity to distinguish them from other tick-derived proteins. A reductionist approach to identify defined tick proteins will remain as paramount in the search for defined anti-paralysis vaccines.

Identification and characterization of a histamine-binding lipocalin-like molecule from the relapsing fever tick Ornithodoros turicata

Lipocalins are low molecular weight membrane transporters that are abundantly expressed in the salivary glands and other tissues of ticks. In this study, we identified a lipocalin-like molecule, designated as otlip, from the soft ticks Ornithodoros turicata, the vector for the relapsing fever causing spirochete Borrelia turicatae. We noted that the expression of otlip was developmentally regulated, with adult ticks expressing significantly higher levels in comparison to the larvae or nymphal ticks. Expression of otlip was evident in both fed and unfed O. turicata ticks, with significantly increased expression in the salivary glands in comparison to the midgut or ovary tissues. High conservation of the biogenic amine-binding motif was evident in the deduced primary amino acid sequence of Otlip. Protein modelling of Otlip revealed conservation of most of the residues involved in binding histamine or serotonin ligand. In vitro assays demonstrated binding of recombinant Otlip with histamine. Furthermore, prediction of post-translational modifications revealed that Otlip contained phosphorylation and myristoylation sites. Taken together, our study not only provides evidence for the presence of a lipocalin-like molecule in O. turicata ticks but also suggests a role for this molecule in the salivary glands of this medically important vector.

Are Fireworms Venomous? Evidence for the Convergent Evolution of Toxin Homologs in Three Species of Fireworms (Annelida, Amphinomidae)

Amphinomids, more commonly known as fireworms, are a basal lineage of marine annelids characterized by the presence of defensive dorsal calcareous chaetae, which break off upon contact. It has long been hypothesized that amphinomids are venomous and use the chaetae to inject a toxic substance. However, studies investigating fireworm venom from a morphological or molecular perspective are scarce and no venom gland has been identified to date, nor any toxin characterized at the molecular level. To investigate this question, we analyzed the transcriptomes of three species of fireworms-Eurythoe complanata, Hermodice carunculata, and Paramphinome jeffreysii-following a venomics approach to identify putative venom compounds. Our venomics pipeline involved de novo transcriptome assembly, open reading frame, and signal sequence prediction, followed by three different homology search strategies: BLAST, HMMER sequence, and HMMER domain. Following this pipeline, we identified 34 clusters of orthologous genes, representing 13 known toxin classes that have been repeatedly recruited into animal venoms. Specifically, the three species share a similar toxin profile with C-type lectins, peptidases, metalloproteinases, spider toxins, and CAP proteins found among the most highly expressed toxin homologs. Despite their great diversity, the putative toxins identified are predominantly involved in three major biological processes: hemostasis, inflammatory response, and allergic reactions, all of which are commonly disrupted after fireworm stings. Although the putative fireworm toxins identified here need to be further validated, our results strongly suggest that fireworms are venomous animals that use a complex mixture of toxins for defense against predators.

Exploring the molecular complexity of Triatoma dimidiata sialome

Triatoma dimidiata, a Chagas disease vector widely distributed along Central America, has great capability for domestic adaptation as the majority of specimens caught inside human dwellings or in peridomestic areas fed human blood. Exploring the salivary compounds that overcome host haemostatic and immune responses is of great scientific interest. Here, we provide a deeper insight into its salivary gland molecules. We used high-throughput RNA sequencing to examine in depth the T. dimidiata salivary gland transcriptome. From >51 million reads assembled, 92.21% are related to putative secreted proteins. Lipocalin is the most abundant gene family, confirming it is an expanded family in Triatoma genus salivary repertoire. Other putatively secreted members include phosphatases, odorant binding protein, hemolysin, proteases, protease inhibitors, antigen-5 and antimicrobial peptides. This work expands the previous set of functionally annotated sequences from T. dimidiata salivary glands available in NCBI from 388 to 3815. Additionally, we complemented the salivary analysis through proteomics (available data via ProteomeXchange with identifier PXD008510), disclosing the set complexity of 119 secreted proteins and validating the transcriptomic results. Our large-scale approach enriches the pharmacologically active molecules database and improves our knowledge about the complexity of salivary compounds from haematophagous vectors and their biological interactions.

SIGNIFICANCE

Several haematophagous triatomine species can transmit Trypanosoma cruzi, the etiological agent of Chagas disease. Due to the reemergence of this disease, new drugs for its prevention and treatment are considered priorities. For this reason, the knowledge of vector saliva emerges as relevant biological finding, contributing to the design of different strategies for vector control and disease transmission. Here we report the transcriptomic and proteomic compositions of the salivary glands (sialome) of the reduviid bug Triatoma dimidiata, a relevant Chagas disease vector in Central America. Our results are robust and disclosed unprecedented insights into the notable diversity of its salivary glands content, revealing relevant anti-haemostatic salivary gene families. Our work expands almost ten times the previous set of functionally annotated sequences from T. dimidiata salivary glands available in NCBI. Moreover, using an integrated transcriptomic and proteomic approach, we showed a correlation pattern of transcription and translation processes for the main gene families found, an important contribution to the research of triatomine sialomes. Furthermore, data generated here reinforces the secreted proteins encountered can greatly contribute for haematophagic habit, Trypanosoma cruzi transmission and development of therapeutic agent studies.

Gene Duplication and Protein Evolution in Tick-Host Interactions

Ticks modulate their hosts' defense responses by secreting a biopharmacopiea of hundreds to thousands of proteins and bioactive chemicals into the feeding site (tick-host interface). These molecules and their functions evolved over millions of years as ticks adapted to blood-feeding, tick lineages diverged, and host-shifts occurred. The evolution of new proteins with new functions is mainly dependent on gene duplication events. Central questions around this are the rates of gene duplication, when they occurred and how new functions evolve after gene duplication. The current review investigates these questions in the light of tick biology and considers the possibilities of ancient genome duplication, lineage specific expansion events, and the role that positive selection played in the evolution of tick protein function. It contrasts current views in tick biology regarding adaptive evolution with the more general view that neutral evolution may account for the majority of biological innovations observed in ticks.

TSGP4 from Ornithodoros moubata: molecular cloning, phylogenetic analysis and vaccine efficacy of a new member of the lipocalin clade of cysteinyl leukotriene scavengers

Recently obtained evidence indicated that an orthologue of the O. savignyi TSGP4 salivary lipocalin was present in the saliva of O. moubata. TSGP4 is known to act as a cysteinyl leukotrienes scavenger helping in the prevention of inflammation and oedema at the tick bite site. Since this function seems to be crucial for successful tick feeding, the novel O. moubata TSGP4 turned into a potential vaccine target. The purposes of the current work were: (i) to clone and characterize the O. moubata TSGP4 and, (ii) to produce it as recombinant to evaluate its protective efficacy as vaccine antigen. The results of these experiments indicated that the O. moubata TSGP4 shows high sequence and structural identity with the O. savignyi orthologue suggesting identical function in the physiology of the tick-host relationship. The mature native TSGP4 is not immunogenic when it is inoculated to host with tick saliva during feeding, but host vaccination with the recombinant protein TSGP4 in Freund's adjuvants induced strong humoral immune responses that recognized both the recombinant and native TSGP4 and protected the host with a 14.1% efficacy. So, the O. moubata TSGP4 can be considered a silent salivary antigen; however, in the light of the current results, its inclusion in the current repertory of protective antigens to be targeted by anti-tick vaccines could be controversial.

Are ticks venomous animals?

INTRODUCTION

As an ecological adaptation venoms have evolved independently in several species of Metazoa. As haematophagous arthropods ticks are mainly considered as ectoparasites due to directly feeding on the skin of animal hosts. Ticks are of major importance since they serve as vectors for several diseases affecting humans and livestock animals. Ticks are rarely considered as venomous animals despite that tick saliva contains several protein families present in venomous taxa and that many Ixodida genera can induce paralysis and other types of toxicoses. Tick saliva was previously proposed as a special kind of venom since tick venom is used for blood feeding that counteracts host defense mechanisms. As a result, the present study provides evidence to reconsider the venomous properties of tick saliva.

RESULTS

Based on our extensive literature mining and in silico research, we demonstrate that ticks share several similarities with other venomous taxa. Many tick salivary protein families and their previously described functions are homologous to proteins found in scorpion, spider, snake, platypus and bee venoms. This infers that there is a structural and functional convergence between several molecular components in tick saliva and the venoms from other recognized venomous taxa. We also highlight the fact that the immune response against tick saliva and venoms (from recognized venomous taxa) are both dominated by an allergic immunity background. Furthermore, by comparing the major molecular components of human saliva, as an example of a non-venomous animal, with that of ticks we find evidence that ticks resemble more venomous than non-venomous animals. Finally, we introduce our considerations regarding the evolution of venoms in Arachnida.

CONCLUSIONS

Taking into account the composition of tick saliva, the venomous functions that ticks have while interacting with their hosts, and the distinguishable differences between human (non-venomous) and tick salivary proteins, we consider that ticks should be referred to as venomous ectoparasites.

Savicalin, a lipocalin from hemocytes of the soft tick, Ornithodoros savignyi

Savicalin, is a lipocalin found in the hemocytes of the soft tick, Ornithodoros savignyi. It could be assigned to the tick lipocalin family based on BLAST analysis. Savicalin is the first non-salivary gland lipocalin described in ticks. The mature sequence is composed of 188 amino acids with a molecular mass of 21481.9 Da. A homolog for savicalin was found in a whole body EST-library from a related soft tick O. porcinus, while other tick salivary gland derived lipocalins retrieved from the non-redundant sequence database are more distantly related. Homology modeling supports the inclusion of savicalin into the lipocalin family. The model as well as multiple alignments suggests the presence of five disulphide bonds. Two conserved disulphide bonds are found in hard and soft tick lipocalins. A third disulphide bond is shared with the TSGP4-clade of leukotriene C4 binding soft tick lipocalins and a fourth is shared with a lipocalin from the hard tick Ixodes scapularis. The fifth disulphide bond is unique and links strands D-E. Phylogenetic analysis showed that savicalin is a distant relative of salivary gland derived lipocalins, but groups within a clade that is possibly non-salivary gland derived. It lacks the biogenic amine-binding motif associated with tick histamine and serotonin binding proteins. Expression profiles indicate that savicalin is found in hemocytes, midgut and ovaries, but not in the salivary glands. Up-regulation occurs in hemocytes after bacterial challenge and in midguts and ovaries after feeding. Given its tissue distribution and up-regulation of expression, it is possible that this lipocalin functions in tick development after feeding or in an anti-microbial capacity.

Molecular diversity of toxic components from the scorpion Heterometrus petersii venom revealed by proteomic and transcriptome analysis

Scorpion venoms contain a vast untapped reservoir of natural products, which have the potential for medicinal value in drug discovery. In this study, toxin components from the scorpion Heterometrus petersii venom were evaluated by transcriptome and proteome analysis.Ten known families of venom peptides and proteins were identified, which include: two families of potassium channel toxins, four families of antimicrobial and cytolytic peptides,and one family from each of the calcium channel toxins, La1-like peptides, phospholipase A2,and the serine proteases. In addition, we also identified 12 atypical families, which include the acid phosphatases, diuretic peptides, and ten orphan families. From the data presented here, the extreme diversity and convergence of toxic components in scorpion venom was uncovered. Our work demonstrates the power of combining transcriptomic and proteomic approaches in the study of animal venoms.

Der-p2 ( Dermatophagoides pteronyssinus) allergen-like protein from the hard tick Ixodes ricinus - a novel member of ML (MD-2-related lipid-recognition) domain protein family

OBJECTIVE

Expression of the gene encoding Der-p2 allergen-like protein in the castor bean tick Ixodes ricinus is induced by blood intake. Tick Der-p2 allergen-like protein belongs to a diverse family of ML proteins that includes major allergens of house dust mites, human MD-2 or similar proteins from Drosophila melanogaster. In ticks, genes encoding proteins belonging to the ML protein family were identified, but their protein products have not been characterized yet.

METHODS

A gene encoding tick Der-p2 allergen-like protein was amplified from cDNA of engorged I. ricinus female using the gene-specific primers designed on a basis of partial sequences of related allergen-like genes. The tissue and state specific patterns of expression of the gene were analysed. The IgE binding activity of the produced recombinant protein was studied by use of ELISA.

RESULTS

Analysis of the expression pattern showed that the gene encoding the tick Der-p2 allergen-like protein is strongly induced by the bloodmeal in gut and haemolymph throughout all tick developmental stages. Der-p2 allergen-like protein possesses a putative lipid-binding site, according to the comparisons with the related proteins. The ability of tick Der-p2 allergen-like protein to bind immunoglobulin E (IgE) was revealed.

DISCUSSION

The presence of a putative lipid-binding domain in Der-p2 allergen-like protein and its ability to interact with IgE might indicate the involvement of the protein in the tick's immune response.

The Toxicogenomic Multiverse: Convergent Recruitment of Proteins Into Animal Venoms

Throughout evolution, numerous proteins have been convergently recruited into the venoms of various animals, including centipedes, cephalopods, cone snails, fish, insects (several independent venom systems), platypus, scorpions, shrews, spiders, toxicoferan reptiles (lizards and snakes), and sea anemones. The protein scaffolds utilized convergently have included AVIT/colipase/prokineticin, CAP, chitinase, cystatin, defensins, hyaluronidase, Kunitz, lectin, lipocalin, natriuretic peptide, peptidase S1, phospholipase A2, sphingomyelinase D, and SPRY. Many of these same venom protein types have also been convergently recruited for use in the hematophagous gland secretions of invertebrates (e.g., fleas, leeches, kissing bugs, mosquitoes, and ticks) and vertebrates (e.g., vampire bats). Here, we discuss a number of overarching structural, functional, and evolutionary generalities of the protein families from which these toxins have been frequently recruited and propose a revised and expanded working definition for venom. Given the large number of striking similarities between the protein compositions of conventional venoms and hematophagous secretions, we argue that the latter should also fall under the same definition.

The role of saliva in tick feeding

When attempting to feed on their hosts, ticks face the problem of host hemostasis (the vertebrate mechanisms that prevent blood loss), inflammation (that can produce itching or pain and thus initiate defensive behavior on their hosts) and adaptive immunity (by way of both cellular and humoral responses). Against these barriers, ticks evolved a complex and sophisticated pharmacological armamentarium, consisting of bioactive lipids and proteins, to assist blood feeding. Recent progress in transcriptome research has uncovered that hard ticks have hundreds of different proteins expressed in their salivary glands, the majority of which have no known function, and include many novel protein families (e.g., their primary structure is unique to ticks). This review will address the vertebrate mechanisms of these barriers as a guide to identify the possible targets of these large numbers of known salivary proteins with unknown function. We additionally provide a supplemental Table that catalogues over 3,500 putative salivary proteins from various tick species, which might assist the scientific community in the process of functional identification of these unique proteins. This supplemental file is accessble fromhttp://exon.niaid.nih.gov/transcriptome/tick_review/Sup-Table-1.xls.gz.

Ixodes ricinus tick lipocalins: identification, cloning, phylogenetic analysis and biochemical characterization

BACKGROUND

During their blood meal, ticks secrete a wide variety of proteins that interfere with their host's defense mechanisms. Among these proteins, lipocalins play a major role in the modulation of the inflammatory response.

METHODOLOGY/PRINCIPAL FINDINGS

Screening a cDNA library in association with RT-PCR and RACE methodologies allowed us to identify 14 new lipocalin genes in the salivary glands of the Ixodes ricinus hard tick. A computational in-depth structural analysis confirmed that LIRs belong to the lipocalin family. These proteins were called LIR for "Lipocalin from I. ricinus" and numbered from 1 to 14 (LIR1 to LIR14). According to their percentage identity/similarity, LIR proteins may be assigned to 6 distinct phylogenetic groups. The mature proteins have calculated pM and pI varying from 21.8 kDa to 37.2 kDa and from 4.45 to 9.57 respectively. In a western blot analysis, all recombinant LIRs appeared as a series of thin bands at 50-70 kDa, suggesting extensive glycosylation, which was experimentally confirmed by treatment with N-glycosidase F. In addition, the in vivo expression analysis of LIRs in I. ricinus, examined by RT-PCR, showed homogeneous expression profiles for certain phylogenetic groups and relatively heterogeneous profiles for other groups. Finally, we demonstrated that LIR6 codes for a protein that specifically binds leukotriene B4.

CONCLUSIONS/SIGNIFICANCE

This work confirms that, regarding their biochemical properties, expression profile, and sequence signature, lipocalins in Ixodes hard tick genus, and more specifically in the Ixodes ricinus species, are segregated into distinct phylogenetic groups suggesting potential distinct function. This was particularly demonstrated by the ability of LIR6 to scavenge leukotriene B4. The other LIRs did not bind any of the ligands tested, such as 5-hydroxytryptamine, ADP, norepinephrine, platelet activating factor, prostaglandins D2 and E2, and finally leukotrienes B4 and C4.

An insight into the salivary transcriptome and proteome of the soft tick and vector of epizootic bovine abortion, Ornithodoros coriaceus

The salivary glands of blood-sucking arthropods contain a redundant 'magic potion' that counteracts their vertebrate host's hemostasis, inflammation, and immunity. We here describe the salivary transcriptome and proteomics (sialome) of the soft tick Ornithodoros coriaceus. The resulting analysis helps to consolidate the classification of common proteins found in both soft and hard ticks, such as the lipocalins, Kunitz, cystatin, basic tail, hebraein, defensin, TIL domain, metalloprotease, 5'-nucleotidase/apyrase, and phospholipase families, and also to identify protein families uniquely found in the Argasidae, such as the adrenomedullin/CGRP peptides, 7DB, 7 kDa, and the RGD-containing single-Kunitz proteins. Additionally, we found a protein belonging to the cytotoxin protein family that has so far only been identified in hard ticks. Three other unique families common only to the Ornithodoros genus were discovered. Edman degradation, 2D and 1D-PAGE of salivary gland homogenates followed by tryptic digestion and HPLC MS/MS of results confirms the presence of several proteins. These results indicate that each genus of hematophagous arthropods studied to date evolved unique protein families that assist blood feeding, thus characterizing potentially new pharmacologically active components or antimicrobial agents.

Function, mechanism and evolution of the moubatin-clade of soft tick lipocalins

The "moubatin-clade" of soft tick lipocalins, although monophyletic, shows clear signs of paralogy as indicated by the various functions associated with this protein family. This includes anti-platelet (moubatin), anti-complement (OMCI) and toxic (TSGP2) activities in the vertebrate host. In order to understand the evolution of function and how it relates to the various paralogs in this clade, we characterized a number of different proteins in regard to undefined function and mechanism. By utilizing gain-of-function for TSGP2 and loss-of-function for TSGP3, we show that inhibition of collagen-induced platelet aggregation by moubatin and TSGP3 is due to scavenging of thromboxane A2. Moubatin, TSGP2 and TSGP3 are also able to bind leukotriene B4 with high affinity. TSGP2 and TSGP3, but not moubatin, binds complement C5, with kinetics that indicates that conformation change occurs during interaction. A conserved loop and histidine residue in the sequences of OMCI, TSGP2 and TSGP3 are implicated in the interaction with complement C5. The data presented suggest that the ancestral function evolved in this clade was aimed at inhibition of vasoconstriction, platelet aggregation and neutrophil aggregation, primarily by scavenging of thromboxane A2 and leukotriene B4. C5 complement targeting activity evolved within this clade, probably within the Old World Ornithodorinae. The moubatin-clade itself most probably derived from the related histamine and serotonin-binding lipocalin sub-family that is conserved within the Argasidae.

A novel clade of cysteinyl leukotriene scavengers in soft ticks

Inflammation is an important vertebrate defense mechanism against ecto-parasites for which ticks have evolved numerous mechanisms of modulation. AM-33 and TSGP4, related lipocalins from the soft ticks Argas monolakensis and Ornithodoros savignyi bind cysteinyl leukotrienes with high affinity as measured by isothermal titration calorimetry. This was confirmed in a smooth muscle bioassay that measured contraction of guinea pig ileum induced by leukotriene C4 where both proteins inhibited contraction effectively. Conservation of this function in two diverse soft tick genera suggests that scavenging of cysteinyl leukotrienes evolved in the ancestral soft tick lineage. In addition soft ticks also evolved mechanisms that target other mediators of inflammation that include scavenging of histamine, serotonin, leukotriene B4, thromboxane A2, ATP and inhibition of the complement cascade. Inhibitors of blood-coagulation and platelet aggregation were also present in the ancestral soft tick lineage. Because histamine and cysteinyl leukotrienes are mainly produced by mast cells and basophils, and these cells are important in the mediation of tick rejection reactions, these findings indicate an ancient antagonistic relationship between ticks and the immune system. As such, modulation of the hemostatic system as well as inflammation was important adaptive responses in the evolution of a blood-feeding lifestyle in soft ticks.

Structure, function, and evolution of biogenic amine-binding proteins in soft ticks

Two highly abundant lipocalins, monomine and monotonin, have been isolated from the salivary gland of the soft tick Argas monolakensis and shown to bind histamine and 5-hydroxytryptamine (5-HT), respectively. The crystal structures of monomine and a paralog of monotonin were determined in the presence of ligands to compare the determinants of ligand binding. Both the structures and binding measurements indicate that the proteins have a single binding site rather than the two sites previously described for the female-specific histamine-binding protein (FS-HBP), the histamine-binding lipocalin of the tick Rhipicephalus appendiculatus. The binding sites of monomine and monotonin are similar to the lower, low affinity site of FS-HBP. The interaction of the protein with the aliphatic amine group of the ligand is very similar for the all of the proteins, whereas specificity is determined by interactions with the aromatic portion of the ligand. Interestingly, protein interaction with the imidazole ring of histamine differs significantly between the low affinity binding site of FS-HBP and monomine, suggesting that histamine binding has evolved independently in the two lineages. From the conserved features of these proteins, a tick lipocalin biogenic amine-binding motif could be derived that was used to predict biogenic amine-binding function in other tick lipocalins. Heterologous expression of genes from salivary gland libraries led to the discovery of biogenic amine-binding proteins in soft (Ornithodoros) and hard (Ixodes) tick genera. The data generated were used to reconstruct the most probable evolutionary pathway for the evolution of biogenic amine-binding in tick lipocalins.

Distantly related lipocalins share two conserved clusters of hydrophobic residues: use in homology modeling

Background

Lipocalins are widely distributed in nature and are found in bacteria, plants, arthropoda and vertebra. In hematophagous arthropods, they are implicated in the successful accomplishment of the blood meal, interfering with platelet aggregation, blood coagulation and inflammation and in the transmission of disease parasites such as Trypanosoma cruzi and Borrelia burgdorferi.

The pairwise sequence identity is low among this family, often below 30%, despite a well conserved tertiary structure. Under the 30% identity threshold, alignment methods do not correctly assign and align proteins. The only safe way to assign a sequence to that family is by experimental determination. However, these procedures are long and costly and cannot always be applied. A way to circumvent the experimental approach is sequence and structure analyze. To further help in that task, the residues implicated in the stabilisation of the lipocalin fold were determined. This was done by analyzing the conserved interactions for ten lipocalins having a maximum pairwise identity of 28% and various functions.

Results

It was determined that two hydrophobic clusters of residues are conserved by analysing the ten lipocalin structures and sequences. One cluster is internal to the barrel, involving all strands and the 3₁₀ helix. The other is external, involving four strands and the helix lying parallel to the barrel surface. These clusters are also present in RaHBP2, a unusual "outlier" lipocalin from tick Rhipicephalus appendiculatus. This information was used to assess assignment of LIR2 a protein from Ixodes ricinus and to build a 3D model that helps to predict function. FTIR data support the lipocalin fold for this protein.

Conclusion

By sequence and structural analyzes, two conserved clusters of hydrophobic residues in interactions have been identified in lipocalins. Since the residues implicated are not conserved for function, they should provide the minimal subset necessary to confer the lipocalin fold. This information has been used to assign LIR2 to lipocalins and to investigate its structure/function relationship. This study could be applied to other protein families with low pairwise similarity, such as the structurally related fatty acid binding proteins or avidins.

Comparative sialomics between hard and soft ticks: implications for the evolution of blood-feeding behavior

Ticks evolved various mechanisms to modulate their host's hemostatic and immune defenses. Differences in the anti-hemostatic repertoires suggest that hard and soft ticks evolved anti-hemostatic mechanisms independently, but raise questions on the conservation of salivary gland proteins in the ancestral tick lineage. To address this issue, the sialome (salivary gland secretory proteome) from the soft tick, Argas monolakensis, was determined by proteomic analysis and cDNA library construction of salivary glands from fed and unfed adult female ticks. The sialome is composed of approximately 130 secretory proteins of which the most abundant protein folds are the lipocalin, BTSP, BPTI and metalloprotease families which also comprise the most abundant proteins found in the salivary glands. Comparative analysis indicates that the major protein families are conserved in hard and soft ticks. Phylogenetic analysis shows, however, that most gene duplications are lineage specific, indicating that the protein families analyzed possibly evolved most of their functions after divergence of the two major tick families. In conclusion, the ancestral tick may have possessed a simple (few members for each family), but diverse (many different protein families) salivary gland protein domain repertoire.

An insight into the sialome of the soft tick, Ornithodorus parkeri

While hard ticks (Ixodidae) take several days to feed on their hosts, soft ticks (Argasidae) feed faster, usually taking less than 1h per meal. Saliva assists in the feeding process by providing a cocktail of anti-hemostatic, anti-inflammatory and immunomodullatory compounds. Saliva of hard ticks has been shown to contain several families of genes each having multiple members, while those of soft ticks are relatively unexplored. Analysis of the salivary transcriptome of the soft tick Ornithodorus parkeri, the vector of the relapsing fever agent Borrelia parkeri, indicates that gene duplication events have led to a large expansion of the lipocalin family, as well as of several genes containing Kunitz domains indicative of serine protease inhibitors, and several other gene families also found in hard ticks. Novel protein families with sequence homology to insulin growth factor-binding protein (prostacyclin-stimulating factor), adrenomedulin, serum amyloid A protein precursor and similar to HIV envelope protein were also characterized for the first time in the salivary gland of a blood-sucking arthropod. The sialotranscriptome of O. parkeri confirms that gene duplication events are an important driving force in the creation of salivary cocktails of blood-feeding arthropods, as was observed with hard ticks and mosquitoes. Most of the genes coding for expanded families are homologous to those found in hard ticks, indicating a strong common evolutionary path between the two families. As happens to all genera of blood-sucking arthropods, several new proteins were also found, indicating the process of adaptation to blood feeding still continues to recent times.

A proteomic approach to the identification of salivary proteins from the argasid ticks Ornithodoros moubata and Ornithodoros erraticus

The saliva of ticks contains anti-haemostatic, anti-inflammatory and immunomodulatory molecules that allow these parasites to obtain a blood meal from the host and help tick-borne pathogens to infect the vertebrate host more efficiently. This makes the salivary molecules attractive targets to control ticks and tick-borne pathogens. Although Ornithodoros moubata and O. erraticus are important argasid ticks that transmit severe diseases, to date only a few of their salivary proteins have been identified. Here we report our initial studies using proteomic approaches to characterize the protein profiles of salivary gland extracts (SGE) from these two argasids. The present work describes the proteome of the SGEs of both tick species, their antigenic spots, and the identification of several of their proteins. The whole number of identifications was low despite the good general quality of the peptide mass maps obtained. In the O. moubata SGE, 18 isoforms of a protein similar to O. savignyi TSGP1 were identified. In the O. erraticus SGE we identified 6 novel proteins similar to unknown secreted protein DS-1 precursor, NADPH dehydrogenase subunit 5, proteasome alpha subunit, ATP synthase F0 subunit 6, lipocalin and alpha tubulin. Finally, the current drawbacks of proteomics when applied to the identification of acarine peptides and proteins are discussed.

Tick anti-hemostatics: targets for future vaccines and therapeutics

For ticks, a significant obstacle in obtaining a blood meal is counteracting the hemostatic system of the host. To this end, ticks have developed a broad array of anti-hemostatics, which is reflected in the presence of structurally related tick proteins with different functions. Disruption of blood flow which blocks successful tick feeding makes anti-hemostatics attractive targets for anti-tick vaccines. Moreover, the limited number of drugs currently available for a range of important cardio-vascular diseases makes ticks a potential source of novel therapeutics. This review aims to summarize the key features of tick anti-hemostatics, their structures, mode of action and possible future application as vaccines and novel therapeutic agents.

The structure of OMCI, a novel lipocalin inhibitor of the complement system

The complement (C) system is a potent innate immune defence system against parasites. We have recently characterised and expressed OmCI, a 16 kDa protein derived from the soft tick Ornithodoros moubata that specifically binds C5, thereby preventing C activation. The structure of recombinant OmCI determined at 1.9 A resolution confirms a lipocalin fold and reveals that the protein binds a fatty acid derivative that we have identified by mass spectrometry as ricinoleic acid. We propose that OmCI could sequester one of the fatty acid-derived inflammatory modulators from the host plasma, thereby interfering with the host inflammatory response to the tick bite. Mapping of sequence differences between OmCI and other tick lipocalins with different functions, combined with biochemical investigations of OmCI activity, supports the hypothesis that OmCI acts by preventing interaction with the C5 convertase, rather than by blocking the C5a cleavage site.

Biochemical perspectives on paralysis and other forms of toxicoses caused by ticks

Tick toxicoses, of which paralysis is the most widespread and dominant form, are important elements of pathogenesis induced by ticks. Tick paralysis is the most widespread and dominant form of tick toxicoses. Non-paralytic forms of tick toxicoses do occur and evidence suggests that these forms of toxicoses are not evolutionary related. While functional significance has been suggested for tick toxins, the advantages for tick survival in general are not clear. This review considers the molecular nature of tick toxins, the possibility that tick toxins have originated more than once independently and whether these toxins could have unrecognized benign functions.

Abducens nerve palsy following a tick bite: A case report

Neuromuscular paralysis caused by salivary proteins of ticks is a well-known complication after tick bites in Australia, North America, and South Africa. Symptoms may include general weakness, difficulty walking, ascending paralysis, and bulbar paralysis with diplopia, culminating in respiratory failure. In Europe, toxin-mediated paralysis has rarely been noted. We report a case of cranial nerve paralysis with delayed onset after a tick bite in northern Germany.

An annotated catalog of salivary gland transcripts from Ixodes scapularis ticks

Over 8000 expressed sequence tags from six different salivary gland cDNA libraries from the tick Ixodes scapularis were analyzed. These libraries derive from feeding nymphs infected or not with the Lyme disease agent, Borrelia burgdorferi, from unfed adults, and from adults feeding on a rabbit for 6-12 h, 18-24 h, and 3-4 days. Comparisons of the several libraries led to identification of several significantly differentially expressed transcripts. Additionally, over 500 new predicted protein sequences are described, including several novel gene families unique to ticks; no function can be presently ascribed to most of these novel families. Among the housekeeping-associated transcripts, we highlight those enzymes associated with post translation modification of amino acids, particularly those forming sulfotyrosine, hydroxyproline, and carboxyl-glutamic acid. Results support the hypothesis that gene duplication, most possibly including genome duplications, is a major player in tick evolution.

Proteins in the saliva of the Ixodida (ticks): Pharmacological features and biological significance

The saliva of ticks (Suborder Ixodida) is critical to their survival as parasites. A tick bite should result in strong responses from the host defence systems (haemostatic, immune and inflammatory) but tick saliva appears to have evolved to counter these responses. We review current knowledge of tick saliva components, with emphasis on those molecules confirmed to be present in the secreted saliva but including some that have only been confirmed to be present in salivary glands. About 50 tick saliva proteins that are well described in the literature are discussed. These saliva components include enzymes, enzyme inhibitors, amine-binding proteins and cytokine homologues that act as anti-haemostatic, anti-inflammatory or immuno-modulatory agents. Sequence comparisons are illustrated. The importance of tick saliva and the significance of the findings to date are also discussed.

Exploring tick saliva: from biochemistry to ‘sialomes’ and functional genomics

Tick saliva, a fluid once believed to be only relevant for lubrication of mouthparts and water balance, is now well known to be a cocktail of potent anti-haemostatic, anti-inflammatory and immunomodulatory molecules that helps these arthropods obtain a blood meal from their vertebrate hosts. The repertoire of pharmacologically active components in this cocktail is impressive as well as the number of targets they specifically affect. These salivary components change the physiology of the host at the bite site and, consequently, some pathogens transmitted by ticks take advantage of this change and become more infective. Tick salivary proteins have therefore become an attractive target to control tick-borne diseases. Recent advances in molecular biology, protein chemistry and computational biology are accelerating the isolation, sequencing and analysis of a large number of transcripts and proteins from the saliva of different ticks. Many of these newly isolated genes code for proteins with homologies to known proteins allowing identification or prediction of their function. However, most of these genes code for proteins with unknown functions therefore opening the road to functional genomic approaches to identify their biological activities and roles in blood feeding and hence, vaccine development to control tick-borne diseases.

Complement inhibitor of C5 activation from the soft tick Ornithodoros moubata

Blood-feeding ticks must control C activation or be damaged by the host inflammatory response. We report the characterization and expression of a novel, relatively small, broad-acting C inhibitory protein (termed OmCI) from the soft tick Ornithodoros moubata. The native 17-kDa nonglycosylated protein inhibits both human and guinea pig classical and alternative C activation pathways. The IC50 values for each pathway were 12 and 27 nM, respectively, in hemolytic assays using human serum diluted 40-fold. The cDNA encodes a protein of 168 aa, including an 18-aa secretion signal sequence that is absent in the mature form. The inhibitor has 46% amino acid identity with moubatin, a platelet aggregation inhibitor also from O. moubata that is an outlying member of the lipocalin family. Native OmCI had no inhibitory effect on the addition of C8 and C9 to preformed C5b-C7 and C5b-C8 to form the membrane attack complex and no effect on the rate of C3a production by the C3 convertase enzymes C4bC2a, C3(H2O)Bb, or C3bBb. Both recombinant and native OmCI abolish production of C5a by human classical (C4bC3bC2a) and alternative (C3bC3bBb) C5 convertases. Addition of excess C5 but not C3 competes away the inhibitory activity of OmCI, indicating that OmCI targets C5 itself rather than inhibiting the C5 convertase C4bC3bC2a itself. Direct binding of OmCI to C5 was demonstrated by Western blotting and gel filtration chromatography using 125I-labeled proteins. OmCI is the first lipocalin family member shown to inhibit C and also the first natural inhibitor that specifically targets the C5 activation step.

Molecular crowding as a mechanism for tick secretory granule biogenesis

During feeding ticks secrete bioactive components into the host to counter-act its immune and hemostatic defense systems. These bioactive components are stored in secretory granules that are secreted during feeding in an exocrine stimulus-response type of mechanism. All proteins destined for secretion are packaged into these granules during granule biogenesis. Up to date no mechanism for granule biogenesis has been proposed, except to note that biogenesis occurs under conditions of high protein and calcium concentrations in an acidic environment. Previously, the most abundant proteins (TSGPs) found in the salivary glands of the soft tick, Ornithodoros savignyi, were suggested to play a part in granule biogenesis, based on their high abundance. The TSGPs are part of the lipocalin family, of which numerous members have been identified in ticks. We consider here the high concentrations of the TSGPs in salivary glands and what effect this will have on the crowded environment inside the secretory granules. It is shown that the TSGPs occur at concentrations that will lead to molecular crowding of which one result is the non-specific aggregation of components to reduce crowding effects. Aggregation of proteins as a mechanism of granule biogenesis has been proposed before, but not in terms of molecular crowding. We thus propose molecular crowding as the general mechanism of granule biogenesis, in tick secretory granules, but can also be extended to other forms of secretory granules in general.

Exon-intron structure of outlier tick lipocalins indicate a monophyletic origin within the larger lipocalin family

All tick proteins assigned to the lipocalin family lack the structural conserved regions (SCRs) that are characteristic of the kernel lipocalins and can thus be classified as outliers. These tick proteins have been assigned to the tick lipocalin family based on database searches that indicated homology between tick sequences and the fact that the histamine binding protein (HBP2) from the hard tick Rhipicephalus appendiculatus (Ixodidae) shows structural similarity to the lipocalin fold. Sequence identity between kernel and outlier lipocalins falls below 20% and the question raised is whether the outlier and kernel lipocalins are truly homologous. More specifically in the case of the tick lipocalins, whether their structural fold is derived from the lipocalin fold or whether convergent evolution resulted in the generation of the basic lipocalin-like fold which consists of an eight stranded continuous anti-parallel beta-barrel terminated by a C-terminal alpha-helix that lies parallel to the barrel. The current study determined the gene structure for HBP2 and TSGP1, TSGP2 and TSGP4, lipocalins identified from the soft tick Ornithodoros savignyi (Argasidae). All tick lipocalins have four introns (A-D) with conserved positions and phases within the tick lipocalin sequence alignment. The positions and phase information are also conserved with regard to the rest of the lipocalin family. Phylogenetic analysis using this information shows conclusively that tick lipocalins are evolutionary related to the rest of the lipocalin family. Tick lipocalins are grouped within a monophyletic clade that indicates a monophyletic origin within the tick lineage and also group with the other arthropod lipocalins in a larger clade. Phylogenetic analysis of sequence alignments based on conserved secondary structure of the lipocalin fold support the conclusions from the gene structure trees. These results indicate that exon-intron arrangement can be useful for the inclusion of outlier lipocalins within the larger lipocalin family.

Adaptation of ticks to a blood-feeding environment: evolution from a functional perspective

Ticks had to adapt to an existing and complex vertebrate hemostatic system from being free-living scavengers. A large array of anti-hemostatic mechanisms evolved during this process and includes blood coagulation as well as platelet aggregation inhibitors. Several questions regarding tick evolution exist. What was the nature of the ancestral tick? When did ticks evolve blood-feeding capabilities? How did these capabilities evolve? Did host specificity influence the adaptation of ticks to a blood-feeding environment? What are the implications of tick evolution for future research into tick biology and vaccine development? We investigate these questions in the light of recent research into protein superfamilies from tick saliva. Our conclusions are that the main tick families adapted independently to a blood-feeding environment. This is supported by major differences observed in all processes involved with blood-feeding for hard and soft ticks. Gene duplication events played a major role in the evolution of novel protein functions involved in tick-host interactions. This occurred during the late Cretaceous and was stimulated by the radiation of birds and placental mammals, which provided numerous new niches for ticks to adapt to a new lifestyle. Independent adaptation of the main tick families to a blood-feeding environment has several implications for future tick research in terms of tick genome projects and vaccine development.