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

Kinins 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. Furthermore, ticks have an expanded number of kinin paracopies in the kinin gene. Silencing the kinin receptor (KR) in females of Rhipicephalus 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. We determined the activities of endogenous kinins on the KR, a G protein‐coupled receptor, and identified potent peptidomimetics. Fourteen predicted R. microplus kinins (Rhimi‐K), and 11 kinin analogs containing aminoisobutyric acid (Aib) were tested. The latter incorporated tick kinin sequences and/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 and 1.1 nM, respectively, matching the EC₅₀ of the most potent tick kinin, Rhimi‐K‐14 (QDSFNPWGa) (EC₅₀ = 1 nM). The potent analog 2415 ([Aib]FR[Aib]WGa, EC₅₀ = 6.8 nM) includes both Aib molecules for resistance to peptidases and a positively charged residue, R, for enhanced water solubility and amphiphilic character. These tick kinins and pseudopeptides expand the repertoire of reagents for tick physiology and toxicology towards finding novel targets for tick management.