Evasin-3-like anti-chemokine activity in salivary gland extracts of ixodid ticks during blood-feeding: a new target for tick control.

Ticks exploit many evasion mechanisms to circumvent the immune control of their hosts including subversion of the communication language between cells of the immune system provided by chemokines and other cytokines. One subversive molecule secreted in the saliva of Rhipicephalus sanguineus is Evasin-3, a structurally unique 7 kDa protein that selectively binds the neutrophil chemoattractants, CXCL8 and (with lower affinity) CXCL1. We compared anti-human CXCL8 and anti-mouse CXCL1/KC activities in salivary gland extracts prepared from adult Amblyomma variegatum, Rhipicephalus appendiculatus and Dermacentor reticulatus ticks during blood-feeding. Both anti-CXCL8 activity and anti-CXCL1 activity were detected in all species and in both adult females and males, with consistently higher activity levels against CXCL8. These results suggest that Evasin-3-like activity is common amongst metastriate ixodid tick species, and provide further evidence of the importance to ticks in controlling neutrophils during blood-feeding. As such, Evasin-3 offers a new target for anti-tick vaccine development.

A tick homologue of the human Ki nuclear autoantigen.

A clone isolated from a tick salivary gland cDNA library encodes a homologue of the human Ki lupus autoantigen, a protein of unknown function that is related to the subunits of the PA28 proteasome activator. The Ki sequences appear to be well conserved between mammals and invertebrates, with 55% identity between the tick and human primary structures. This is the first report of a Ki homologue in invertebrates.

Structure of a D-protein gene and amino-acid sequences of the highly repetitive D-proteins secreted by the accessory glands of the mealworm beetle.

The D-group proteins form the major component of the proteinaceous secretion of the tubular accessory glands of the yellow mealworm beetle, Tenebrio molitor. In a previous paper, we reported the sequence of two D-protein cDNAs and their inferred translation products. Both proteins contain three highly repetitive domains (A, A' and B). In this paper, we present the cDNA-inferred sequences of 8 more D-proteins, none of which contains an A' domain. We also present the structure of a D-protein gene. Southern analysis suggests that genes coding for an A' domain are relatively rare. Genes with a total of 7 or 8 (A + B domain) repeats seem most common.

A tick homologue of the human DNA helicase II 70-kDa subunit.

A clone isolated from a Rhipicephalus appendiculatus salivary gland cDNA library encodes a homologue of the 70-kDa subunit of the mammalian Ku protein, an ATP-dependent DNA helicase. The tick homologue appears to be more closely related to the mammalian protein than to the only other p70 homologue reported in arthropods, the inverted repeat binding protein (IRBP) in the fruitfly, Drosophila melanogaster.

Tick histamine-binding proteins: lipocalins with a second binding cavity.

Tick histamine-binding proteins (HBPs) are lipocalins with two binding pockets. One of these binds histamine with a high affinity and is found at the position expected from other lipocalins, adjacent to the omega-loop at the open-end of the beta-barrel. A second binding cavity, which is a low-affinity site for histamine in one of the HBPs, is located at the end of the barrel that is closed off in other lipocalins. In order to create the second site, the 'closed-end' region has undergone a major reconstruction. Typical lipocalin characteristics, such as the 3(10) helix and a structural cluster of highly conserved residues, have been lost, while an alpha-helix now shields the cavity from the exterior. The prominence of acidic residues in the binding pockets is another distinctive characteristic of HBPs. Whereas most lipocalins have highly hydrophobic binding cavities designed to bind lipophilic compounds, HBPs have evolved to trap cationic, hydrophilic molecules.

cDNA-inferred amino-acid sequence of a C protein, a heparin-binding, basic secretion product of the tubular accessory sex glands of the mealworm beetle, Tenebrio molitor.

C proteins represent one of the four major protein groups secreted by the tubular accessory glands of male mealworm beetles (Tenebrio molitor). They are basic proteins with an apparent molecular mass of 21.9 kDa. In this paper we present the deduced amino-acid sequence of two, almost identical C proteins, termed C1 and C2. The C proteins contain a consensus sequence for a heparin-binding site, and they are efficiently purified from accessory gland homogenates by heparin-affinity chromatography. No sequence resemblance was found with other proteins in the databases, but their high avidity for heparin suggests a possible involvement of the C proteins in sperm capacitation.

The B proteins secreted by the tubular accessory sex glands of the male mealworm beetle, Tenebrio molitor, have sequence similarity to moth pheromone-binding proteins.

B proteins represent one of the four major protein groups secreted by the tubular accessory glands of adult, male mealworm beetles. They are acidic proteins with an apparent molecular mass of 18.8 kDa. In this paper we present the deduced amino-acid sequences of two, almost identical B proteins, termed B1 and B2. The mature proteins are 118 amino acids long. They contain 11 (B2) or 12 (B1) possible phosphorylation sites and are rich in glutamic acid (16%). Lectin binding experiments indicate the presence of asparagine linked carbohydrate. The secondary structure of the B proteins is predicted to be almost completely alpha-helical. The B proteins show significant sequence resemblance to a group of pheromone- and odorant-binding proteins in moths and Drosophila, suggesting a role as carrier proteins for lipids.

Tick histamine-binding proteins: isolation, cloning, and three-dimensional structure.

High-affinity histamine-binding proteins (HBPs) were discovered in the saliva of Rhipicephalus appendiculatus ticks. Their ability to outcompete histamine receptors indicates that they suppress inflammation during blood feeding. The crystal structure of a histamine-bound HBP, determined at 1.25 A resolution, reveals a lipocalin fold novel in containing two binding sites for the same ligand. The sites are orthogonally arranged and highly rigid and form an internal surface of unusual polar character that complements the physicochemical properties of histamine. As soluble receptors of histamine, HBPs offer a new strategy for controlling histamine-based diseases.

A high affinity serotonin- and histamine-binding lipocalin from tick saliva.

To overcome the inflammatory response in its host, the cattle-feeding, brown ear tick secretes histamine-binding proteins into the feeding site. These proteins are beta-barrels with two internal binding sites: a high-affinity (H) site for histamine and a site (L) for which the natural ligand is unknown. Here we report a related protein (SHBP), secreted by a rodent- and cattle-feeding tick, that traps both histamine and serotonin. The histamine-binding H site is well conserved in SHBP, whereas residue changes in the L-like site are consistent with binding of the bulkier serotonin molecule. As histamine is a key inflammatory mediator in cattle, while serotonin takes on this role in rodents, the diversification of these tick proteins may reflect host adaptation.

Amino acid sequence of Sp23, a structural protein of the spermatophore of the mealworm beetle, Tenebrio molitor.

In this paper we present the amino acid sequence of Sp23, a structural protein of the spermatophore of the mealworm beetle (Tenebrio molitor). This is the first report of the primary structure of a spermatophorin. The protein is rich in proline (24%), relatively rich in tyrosine (9%) and glutamine (10%), and does not contain sulfur-containing amino acids. In the carboxyl-terminal half of the protein a peptide motif is repeated which is similar to a repetitive motif in a group of dipteran chorion proteins.

Vector-host interactions in disease transmission.

Tick-borne spirochetes include borreliae that cause Lyme disease and relapsing fever in humans. They survive in a triangle of parasitic interactions between the spirochete and its vertebrate host, the spirochete and its tick vector, and the host and the tick. Until recently, the significance of vector-host interactions in the transmission of arthropod-borne disease agents has been overlooked. However, there is now compelling evidence that the pharmacological activity of tick saliva can have a profound effect on pathogen transmission both from infected tick to uninfected host, and from infected host to uninfected tick. The salivary glands of ticks provide a pharmacopoeia of anti-inflammatory, anti-haemostatic and anti-immune molecules. These include bioactive proteins that control histamine, bind immunoglobulins, and inhibit the alternative complement cascade. The effect of these molecules is to provide a privileged site at the tick-host interface in which borreliae and other tick-borne pathogens are sheltered from the normal innate and acquired host immune mechanisms that combat infections. Understanding the key events at the tick vector-host interface, that promote spirochete infection and transmission, will provide a better understanding of the epidemiology and ecology of these important human pathogens.