Structure-activity relationships for in vitro diuretic activity of CAP2b in the housefly

Authors: Nachman, Ronald; COAST, GEOFFREY - BIRBECK COLLEGE, LONDON

Submitted to: Peptides
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2006
Publication Date: 1/15/2007
Citation: Nachman, R.J., Coast, G.M. 2007. Structure-activity relationships for in vitro diuretic activity of CAP2b in the housefly. Peptides. 28:57-61.

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 insect pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as potent messengers in insects to regulate vital functions. Nevertheless, neuropeptides in and of themselves hold little promise as pest control agents because of susceptibility to being degraded in the target pest. Neuropeptide mimics must be designed that resist degradation by enzymes in the digestive tract and blood of pest insects and interact with the active site within agricultural or medical pests by over-activating or blocking critical, neuropeptide-regulated life functions. We report on the identification of chemical requirements for the fluid secretion activity of the ‘CAP2b’ class of insect neuropeptides in the housefly. This data will aid in the design of neuropeptide-like compounds capable of disrupting critical life functions in flies and other insects. This work brings us one step closer to the development of practical neuropeptide-like substances that will effectively control insect pests in an environmentally friendly fashion.

Technical Abstract: A series of truncated and Ala-replacement analogs of the peptide Manse-CAP2b (pELYAFPRV-NH2) were assayed for diuretic activity on Malpighian tubules of the housefly Musca domestica. The C-terminal hexapeptide proved to be the active core, the minimum sequence required to retain significant diuretic activity. However, full activity required the C-terminal heptapeptide, which was equipotent with the most active of the native housefly CAP2b peptides. Replacement of Arg7 and Val8 with Ala led to inactivity and a large 70-fold drop in potency, respectively, indicating that these were critical residues. The Leu2 was semi-critical, where a 6-fold loss in potency was observed. Conversely, the replacement of all other residues with Ala led to much smaller effects on potency and these positions were considered to be non-critical. This structure-activity relationship data can aid in the design of mimetic agonist/antagonist analogs of this diuretic peptide family with enhanced biostability and bioavailability as tools for arthropod endocrinologists and as potential pest management agents capable of disrupting the water balance in pest flies.