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doi:10.1016/j.peptides.2008.07.006

Conformational aspects and hyperpotent agonists of diapause hormone for termination of pupal diapause in the corn earworm

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Qirui Zhang^a, Ronald J. Nachman^b^,^,, Pawel Zubrzak^b and David L. Denlinger^a^,^,

^aDepartment of Entomology, Ohio State University, 318 West 12th Avenue, Columbus, OH 43210, USA

^bAreawide Pest Management Research Unit, Southern Plains Agricultural Research Center, USDA-ARS, 2881 F&D Road, College Station, TX 77845, USA

Received 12 June 2008;

revised 27 June 2008;

accepted 1 July 2008.

Available online 18 July 2008.

Abstract

Diapause hormone (DH) is a peptide well known to induce embryonic diapause in the commercial silkmoth Bombyx mori. More recently, this same neuropeptide was reported to break diapause in pupae of the agriculturally important Heliothis/Helicoverpa complex. In this study we examine the efficacy and potency of a select group of structural analogs of the native hormone in Helicoverpa zea and report the structures of several analogs that are considerably more potent than DH in breaking diapause. Among the most potent analogs (PK-Etz, PK-2Abf, 901) were those with structural components that enhance resistance to peptidases that degrade and inactivate the native peptide in vivo, which may account, at least in part, for the observed increase in potency for these analogs. Analog 901 was previously demonstrated to both enhance biostablility and bioavailability properties in adult heliothines and thus may be a potential candidate for topical application as a diapause-terminating agent. The significant activity observed for two restricted conformation analogs is consistent with an active conformation for diapause hormone that features a transPro within a type I β-turn in the C-terminal region. DH is also known to successfully break diapause only within a fairly narrow temperature range. While DH is effective at 21 °C, it is not effective at 18 °C. Likewise, the analogs were effective at 21 °C but not at 18 °C. By contrast, 20-hydroxyecdysone, a steroid hormone that is also capable of breaking diapause is effective at both temperatures, thus suggesting that DH and the ecdysteroids act through different mechanisms to terminate diapause.

Keywords: Diapause hormone; Diapause termination; Active core analogs; Aminopeptidases; Helicoverpa zea; Active conformation

Article Outline

1. Introduction
2. Materials and methods 2.1. Insect rearing 2.2. Synthesis and characterization of DH/pyrokinin analogs 2.3. H. zea diapause termination bioassay
3. Results 3.1. Termination of pupal diapause by DH analogs 3.2. Dose-response curves for the active analogs 3.3. Comparison of the diapause termination efficacy of the DH analogs at different temperatures
4. Discussion
Acknowledgements
References

Corresponding author. Tel.: +1 979 260 9315; fax: +1 979 260 9377.
Corresponding author. Tel.: +1 614 292 6425; fax: +1 614 292 2180.

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