|XIONG, CAIXING - Texas A&M University|
|YANG, YUNLONG - Texas A&M University|
|NACHMAN, RONALD - Retired ARS Employee|
|PIETRANTONIO, PATRICIA - Texas A&M University|
Submitted to: Peptides
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2021
Publication Date: N/A
Interpretive Summary: Because of problems with the development of resistance to conventional pesticides, there is a critical need for new concepts and alternative approaches in controlling tick pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as potent hormone messengers in insects and ticks to regulate vital functions. Nevertheless, neuropeptides in and of themselves hold little promise as pest control agents because of their susceptibility to being degraded in the target pest and inability to penetrate the outer shell of insects and ticks. These obstacles may be overcome by designing stable mimics of these neuropeptide hormones that interact with the active site within the agricultural pest. In this study, we describe the identification of the first neuropeptide gene from the southern cattle tick that plays critical roles in life processes in related pest insects and ticks. Neuropeptide mimics were designed and evaluated, and several were capable of disrupting critical life processes in ticks. The research will facilitate development of practical neuropeptide-like substances that can function as environmentally friendly and effective agents for the control of pest tick populations that spread disease in livestock.
Technical Abstract: Pyrokinins (PKs) are pleiotropic neuropeptides that play significant roles in invertebrate 14 physiology. Although functions of PKs are known in insects, there is a lack of knowledge in PK-15 encoding genes and their functions in ticks. Herein the first tick complete cDNAs of the 16 capability (capa) gene were cloned from the southern cattle tick, Rhipicephalus microplus 17 (Acari: Ixodidae), and the blacklegged tick, Ixodes scapularis. Each cDNA encoded one 18 perivicerokinin (PVK) peptide and five different pyrokinins. Two PKs were identical in 19 sequence in the two species. The three PKs unique to R. microplus (Rhimi-PK1, -PK2, and -20 PK5) were tested on the recombinant R. microplus pyrokinin receptor for their dose-responses 21 using a calcium bioluminescence assay. The Rhimi-PKs showed dose-dependent agonistic 22 activities with EC50s ranging from 101-207 nM. In addition, twenty PK analogs designed for 23 enhanced bioavailability and biostability were tested on the receptor. Five of these were designed 24 based on the sequences of the three unique Rhimi-PKs. Eight PK analogs were also agonists; 25 four of them had EC50 ranging from 401 nM-1.9 µM and exhibited comparable efficacy to the 26 native Rhimi-PKs. The structure-activity relationships (SAR) of all analogs were analyzed. Our 27 results suggested that a positively charged, basic lysine at the variable position X of the PK 28 active core (FXPRLamide) conferred enhanced affinity to the analogs in their interaction with 29 the tick receptor. These analogs are promising tools to elucidate the pyrokinin function in ticks in 30 vivo as these analogs are expected to have prolonged hemolymph residence time in comparison 31 to the native peptides.