Abstract
During blood-feeding, mosquito saliva is injected into the skin to facilitate blood meal acquisition. D7 proteins are among the most abundant components of the mosquito saliva. Here we report the ligand binding specificity and physiological relevance of two D7 long proteins from Culex quinquefasciatus mosquito, the vector of filaria parasites or West Nile viruses. CxD7L2 binds biogenic amines and eicosanoids. CxD7L1 exhibits high affinity for ADP and ATP, a binding capacity not reported in any D7. We solve the crystal structure of CxD7L1 in complex with ADP to 1.97 Å resolution. The binding pocket lies between the two protein domains, whereas all known D7s bind ligands either within the N- or the C-terminal domains. We demonstrate that these proteins inhibit hemostasis in ex vivo and in vivo experiments. Our results suggest that the ADP-binding function acquired by CxD7L1 evolved to enhance blood-feeding in mammals, where ADP plays a key role in platelet aggregation.
Highlights
During blood-feeding, mosquito saliva is injected into the skin to facilitate blood meal acquisition
We show that CxD7L1 and CxD7L2 act as platelet aggregation inhibitors ex vivo and interfere with blood hemostasis in vivo supporting the hypothesis that the binding of adenosine 5′-diphosphate (ADP) by CxD7L1 helped C. quinquefasciatus to evolve from blood feeding on birds, where serotonin plays a key role in aggregation, to blood feeding on mammals where ADP is a key mediator of platelet aggregation
In previous studies[7,8], C. quinquefasciatus salivary gland cDNA libraries were sequenced resulting in the identification of 14 cDNA clusters with high sequence similarity to the previously known D7 long forms (D7clu[1]: AF420269 and D7clu[12]: AF420270) and a D7 short form (D7Clu[32], AF420271)
Summary
During blood-feeding, mosquito saliva is injected into the skin to facilitate blood meal acquisition. Our results suggest that the ADP-binding function acquired by CxD7L1 evolved to enhance blood-feeding in mammals, where ADP plays a key role in platelet aggregation. Culex quinquefasciatus (Diptera: Culicidae), commonly known as the southern house mosquito, is a vector of medical and veterinary importance of filaria parasites, including Wuchereria bancrofti and Dirofilaria immitis[1,2] and avian malaria parasites (Plasmodium relictum)[3]. It can transmit several arboviruses including Rift Valley fever, West Nile, St. Louis or Western equine encephalitis viruses[4,5]. We show that CxD7L1 and CxD7L2 act as platelet aggregation inhibitors ex vivo and interfere with blood hemostasis in vivo supporting the hypothesis that the binding of ADP by CxD7L1 helped C. quinquefasciatus to evolve from blood feeding on birds, where serotonin plays a key role in aggregation, to blood feeding on mammals where ADP is a key mediator of platelet aggregation
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