Toward an Understanding of the Molecular Mechanism for Successful Blood Feeding by Coupling Proteomics Analysis with Pharmacological Testing of Horsefly Salivary Glands

Abstract

Horseflies are economically important blood-feeding arthropods and also a nuisance for humans and vectors for filariasis. They rely heavily on the pharmacological properties of their saliva to get a blood meal and suppress immune reactions of hosts. Little information is available on antihemostatic substances in horsefly salivary glands; especially no horsefly immune suppressants have been reported. By proteomics or peptidomics and coupling transcriptome analysis with pharmacological testing, several families of proteins or peptides, which act mainly on the hemostatic system or immune system of the host, were identified and characterized from 30,000 pairs salivary glands of the horsefly Tabanus yao (Diptera, Tabanidae). They are: (i) a novel family of inhibitors of platelet aggregation including two members, which possibly inhibit platelet aggregation by a novel mechanism and act on platelet membrane, (ii) a novel family of immunosuppressant peptides including 12 members, which can inhibit interferon-␥ production and increase interleukin-10 secretion, (iii) a serine protease inhibitor with 56 amino acid residues containing anticoagulant activity, (iv) a serine protease with anticoagulant activity, (v) a protease with fibrinogenolytic activity, (vi) three families of antimicrobial peptides including six members, (vii) a hyaluronidase, (viii) a vasodilator peptide, which is an isoform of vasotab identified from Hybomitra bimaculata, and interestingly (ix) two metallothioneins, which are the first metallothioneins reported from invertebrate salivary glands. The current work will facilitate the understanding of the molecular mechanisms of the ectoparasite-host relationship and help in identifying novel vaccine targets and novel leading pharmacological compounds. Molecular & Cellular Proteomics 7:582-590, 2008.

Anti-thrombosis Repertoire of Blood-feeding Horsefly Salivary Glands

“…They act as thrombin inhibitors and vasodilators, respectively. Among them, peaks 5.1 and 5.2 are tabkunin 1 and vasotab TY 1, respectively; they have been reported in our previous work (19).…”

“…Until now, seven platelet aggregation inhibitors have been identified from this horsefly. A fibrinogenolytic protein with a molecular weight of 36 (tabfiblysin) (19), which is different from the current six fibrinogenolytic proteins with molecular weight of 26, has been found from this horsefly in our previous report.…”

“…1, K-M). In our previous report, two platelet aggregation inhibitors (tabinhibitin 1 and -2) were identified from the SGE of the horsefly T. yao (19). Until now, seven platelet aggregation inhibitors have been identified from this horsefly.…”

“…All the RGD motifs are positioned in a loop bracketed by cysteine residues as found in other platelet aggregation inhibitors such as variabilin (31), decorsin (32), ornatin (33), and snake disintegrins (34 -36); although tabinhibitins do not share similarity with those known platelet aggregation inhibitors. Tabinhibitins have a molecular weight around 25, whereas other RGD-containing platelet aggregation inhibitors have a much smaller molecular mass (around 5 kDa) (19). Furthermore, most of RGD-containing platelet aggregation inhibitors have a high percentage of cysteine residues, such as variabilin (11%), ornatin (12%), decorsin (15%), and disintegrins (16 -17%) (19).…”

“…As an important hematophagous arthropod, there have been comparatively few studies on antihemostaic substances in horseflies. In our previous report, two platelet inhibitors containing RGD 1 sequence, a thrombin inhibitor peptide and vasoactive peptide have been found in the salivary glands of the horsefly of Tabanus yao (19). A fibrinogenolytic factor with a molecular mass of 36 kDa has been purified from the salivary glands of T. yao; however its amino acid sequence is unknown (19).…”