Abstract

Tick saliva, an essential chemical secretion of the tick salivary gland, is indispensable for tick survival owing to the physiological influence it exerts on the host defence mechanisms via the instrumentality of its cocktail of pharmacologically active molecules (proteins and peptides). Much research about tick salivary proteome has been performed, but how most of the individual salivary proteins are utilized by ticks to facilitate blood acquisition and pathogen transmission is not yet fully understood. In addition, the phosphorylation of some proteins plays a decisive role in their function. However, due to the low phosphorylation level of protein, especially for a small amount of protein, it is more difficult to study phosphorylation. Maybe, for this reason, the scarcity of works on the phosphorylated tick salivary proteomes still abound. Here, we performed a phosphoproteomic analysis of Haemaphysalis longicornis tick saliva via TiO2 enrichment and the most advanced Thermo Fisher Orbitrap Exploris 480 mass spectrometer for identification. A total of 262 phosphorylated tick saliva proteins were identified and were subjected to functional annotation/enrichment analysis. Cellular and metabolic process terms accounted for the largest proportion of the saliva proteins, with the participation of these proteins in vital intracellular and extracellular transport-oriented processes such as vesicle-mediated transport, exocytic process, cell adhesion, and movement of cell/subcellular component. “Endocytosis”, “Protein processing in endoplasmic reticulum”, and “Purine metabolism” were the most significantly enriched pathways. The knockdown (RNAi) of Tudor domain-containing protein (TCP), actin-depolymerizing factors (ADF), programmed cell death protein (PD), and serine/threonine-protein kinase (SPK) resulted in the dissociation of collagen fibers and the pilosebaceous unit, increased inflammatory infiltrates/granulocytes (possibly heterophiles), and the depletion of the epithelium. Ticks injected with SPK dsRNA engorged normally but with a change in skin colour (possibly an autoimmune reaction) and the failure to produce eggs pointing to a possible role of SPK in reproduction and host immune modulation. Ticks injected with ADF dsRNA failed to acquire blood, underscoring the role of ADF in facilitating tick feeding. The results of this study showed the presence of phosphorylation in tick saliva and highlight the roles of salivary phosphoproteins in facilitating tick feeding.

Highlights

  • Ticks are obligate blood-sucking arachnids that utilize their salivary constituents to physiologically influence the defence mechanisms of the host (Cabezas-Cruz and Valdés, 2014)

  • The phosphoproteomic analysis identified a total of 262 phosphorylated tick saliva proteins (Supplementary Table S1)

  • Phosphoproteomic analysis is vital given the essential role of posttranslational modifications in various physiological processes

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Summary

Introduction

Ticks are obligate blood-sucking arachnids that utilize their salivary constituents to physiologically influence the defence mechanisms of the host (Cabezas-Cruz and Valdés, 2014). Ticks, being the most important vectors of pathogens affecting animals, are of great veterinary importance, and constitute enormous public health importance, having been considered only second to mosquitoes as the most significant vectors of human diseases (Dantas-Torres et al, 2012). Their capacity to obtain large volumes of blood over a relatively long period, their longevity and high reproductive capacity, as well as having a broad host spectrum for many species substantially contribute to their success as disease vectors (Šimo et al, 2017). This mode of pathogen transmission promoted via arthropod/tick saliva during blood acquisition has been described as saliva-assisted transmission (SAT) (Nuttall and Labuda, 2008)

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