Purification of a serine protease and evidence for a protein C activator from the saliva of the tick, Ixodes scapularis

Authors

Sivakamasundari Pichu, University of Rhode Island
José M.C. Ribeiro
Thomas N. Mather, University of Rhode IslandFollow
Ivo M.B. Francischetti

Document Type

Article

Date of Original Version

2014

Department

Plant Sciences and Entomology

Abstract

The saliva of ticks is critical to their survival as parasites and hematophagous animals. In this study, we have purified an enzyme with trypsin-like activity from the saliva of the tick vector of Lyme Disease, Ixodes scapularis. This enzyme, named as IXOSP (I. scapularis salivary serine protease), is a 29.9 kDa molecule with N-terminus FPxMVxLRIKxR. A BLAST search identified IXOSP as a secreted serine protease (AAY66740) with a conserved catalytic triad His, Asp, and Ser. In vitro studies demonstrated that IXOSP cleaves chromogenic substrates with arginine in the P₁ position, by a mechanism inhibited by PMSF or aprotinin. Gene expression studies revealed that IXOSP is expressed at different tick developmental stages, including eggs, and unfed or fed adult tick salivary glands, but not in nymphs or in the midgut. While the physiological substrate for IXOSP remains to be identified, we demonstrated that I. scapularis saliva activate protein C (PC) resulting in the production of activated PC, a potent anticoagulant that also regulates a myriad of inflammatory responses through protease activated receptors. In contrast, the salivary glands of Anopheles gambiae, Anopheles stephensi, Anopheles albimanus, Aedes aegypti, Lutzomyia longipalpis, and Phlebotomus ariasi did not activate protein C. These discoveries are discussed in the context of blood coagulation, inflammation and vector–host interactions.

Citation/Publisher Attribution

Pichu, S., Ribero, J. M.C., Mather, T. N., & Francischetti, I. M.B. (2014). Purification of a serine protease and evidence for a protein C activator from the saliva of the tick, Ixodes scapularis. Toxicon, 77, 32-39. doi: 10.1016/j.toxicon.2013.10.025

Available at: https://doi.org/10.1016/j.toxicon.2013.10.025

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