Molecular and pharmacological characterization of the first Chelicerata pyrokinin receptor from a worldwide tick vector of zoonotic pathogens, Rhipicephalus (Boophilus) microplus

Authors: YANG, YUNLONG - Texas A&M University; Nachman, Ronald; PIETRANTONIO, PATRICIA - Texas A&M University

Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2015
Publication Date: 4/15/2015
Citation: Yang, Y., Nachman, R.J., Pietrantonio, P. 2015. Molecular and pharmacological characterization of the first Chelicerata pyrokinin receptor from a worldwide tick vector of zoonotic pathogens, Rhipicephalus (Boophilus) microplus. Insect Biochemistry and Molecular Biology. 60:13-23.

Interpretive Summary: Invertebrate pests have developed resistance to several conventional pesticides, and new approaches are needed for pest management. Although neuropeptides (short chains of amino acids) serve as potent messengers in insects to regulate vital functions, the neuropeptides hold little promise as pest control agents because they can be degraded in the target pest. New, selective control agents may be developed by designing mimics of these neuropeptides that resist degradation and either inhibit or over-stimulate critical neuropeptide-regulated life functions. Research was conducted that, for the first time, characterized the structure and distribution of the active site of the ‘pyrokinin’ (‘PK’) neuropeptide in a tick, specifically an important disease vector known as the ‘cattle fever tick’. Neuropeptides of the ‘PK’ class regulate the critical processes of diapause, muscle contraction and reproduction in insects and this research will aid in the discovery of the precise physiological role they play in ticks. The work further established key differences between the PK receptors of insects and ticks; suggesting that selective mimetic agents can be designed that can distinguish between them. The discoveries revealed in this paper will eventually aid in the design of neuropeptide-like compounds capable of disrupting critical life functions regulated by PK neuropeptides in tick pests. The work brings us one step closer to the development of practical neuropeptide-like substances that will be effective in controlling tick pests in an environmentally friendly fashion.

Technical Abstract: We identified the first pyrokinin receptor (Rhimi-PK-R) from the Chelicerata and analyzed structure-activity relationships of cognate ligand neuropeptides and their analogs. This receptor, which we cloned from larvae of the tick Rhipicephalus microplus (Acari: Ixodidae), is the ortholog of the insect pyrokinin (PK)/ pheromone biosynthesis activating neuropeptide (PBAN)/ diapause hormone (DH) receptor neuropeptide family, based on comparative and phylogenetic analyses. Rhimi-PK-R functional analyses using calcium bioluminescence were performed with a developed stable recombinant CHO-K1 cell line. Rhimi-PK-R was activated by four endogenous PKs from the Lyme disease vector, the tick Ixodes scapularis (EC50s range: 85.4 nM-546 nM) and weakly by another tick PRX-amide peptide, periviscerokinin (PVK) (EC50= 24.5 µM). PK analogs with substitutions of leucine, isoleucine or valine at the C-terminus for three tick PK peptides, Ixosc-PK1, Ixosc-PK2, and Ixosc-PK3, retained their potency on Rhimi-PK-R. Therefore, Rhimi-PK-R is less selective and substantially more tolerant than insect PK receptors of C-terminal substitutions of leucine to isoleucine or valine, a key structural feature that serves to distinguish insect PK from PVK/CAP2b receptors. In females, ovary and synganglion had the highest Rhimi-PK-R relative transcript abundance followed by the rectal sac, salivary glands, Malpighian tubules, and midgut. This is the first pharmacological analysis of a PK/PBAN/DH-like receptor from the Chelicerata, which will now permit the discovery of the endocrinological roles of this neuropeptide family in vectors of vertebrate pathogens.