Cloning and characterization of a plasminogen-binding enolase from the saliva of the argasid tick Ornithodoros moubata

Abstract

Significant amounts of enolase have recently been found in the saliva of the argasid tick Ornithodoros moubata, raising the question as to what the function of enolase in the tick–host interface is. Enolase is a multifunctional glycolytic enzyme known to act as a plasminogen receptor on cellular surfaces, promoting fibrinolysis and extracellular matrix degradation. Fibrinolysis could be important for ticks to dissolve clots that might be formed during feeding as well as to prevent clotting of the ingested blood meal in the tick midgut. Additionally, enolase-mediated extracellular matrix degradation could contribute to the tick feeding lesion. Moreover, previous observations suggested an additional antihaemostatic role for O. moubata enolase as a P-selectin antagonist ligand. Accordingly, the aim of the present study was to investigate the potential role of the O. moubata salivary enolase as a plasminogen receptor and P-selectin ligand, and to evaluate its potential as an antigen target for anti-O. moubata vaccines. The study included the cloning, sequencing and recombinant production of the O. moubata enolase, plasminogen binding and activation assays, P-selectin binding assays, animal immunization trials, and RNAi knockdown of the enolase gene. Here we confirmed that enolase is secreted to the saliva of the tick and provide convincing evidence for a role of this salivary enolase as a plasminogen receptor, most likely stimulating host fibrinolysis and maintaining blood fluidity during tick feeding. The RNAi experiments and immunization trials indicated that enolase could be also involved in the regulation of tick reproduction, suggesting new potential control strategies. Finally, the P-selectin binding experiments demonstrated that this enolase is not a P-selectin ligand.