Activity of native tick kinins and peptidomimetics on the cognate target G protein-coupled receptor from the cattle fever tick, Rhipicephalus microplus (Acari: Ixodidae).

Abstract

BACKGROUND\nKinins are multifunctional neuropeptides that regulate key insect physiological processes such as diuresis, feeding, and ecdysis. However, the physiological roles of kinins in ticks are unclear. Further, ticks have an expanded number of kinin paracopies in the kinin gene. Silencing the kinin receptor in females of R. microplus reduces reproductive fitness. Thus, it appears the kinin signaling system is important for tick physiology, and its disruption may have potential for tick control.\n\n\nRESULTS\nWe determined the activities of endogenous kinins on the kinin receptor, a G protein-coupled receptor (GPCR), and identified potent peptidomimetics. Fourteen predicted R. microplus kinins (Rhimi-K), and eleven kinin analogs containing aminoisobutyric acid (Aib) were tested. The latter either incorporated tick kinin sequences or were modified for enhanced resistance to arthropod peptidases. A high-throughput screen using a calcium fluorescence assay in 384-well-plates was performed. All tested kinins and Aib-analogs were full agonists. The most potent kinin and two kinin analogs were equipotent. Analogs 2414 ([Aib]FS[Aib]WGa) and 2412 ([Aib]FG[Aib]WGa) were the most active with EC50 values of 0.9 nM and 1.1 nM, respectively, matching the EC50 of the most potent tick kinin, Rhimi-K-14 (QDSFNPWGa) (EC50 =\u20091 nM). The potent analog 2415 ([Aib]FR[Aib]WGa, EC50 =\u20096.8 nM) includes both, Aib molecules for resistance to peptidases, and a positively charged residue, R, for enhanced water solubility and amphiphilic character.\n\n\nCONCLUSION\nThese tick kinins and pseudopeptides expand the repertoire of reagents for tick physiology and toxicology towards finding novel targets for tick management. This article is protected by copyright. All rights reserved.