Sequence, characterization and pharmacological analyses of the adipokinetic hormone receptor in the stick insect, Carausius morosus

Gerd Gäde^1*Jinghan Tan²Salwa Afifi²Jean-Paul V Paluzzi²Graham Jackson³Heather Marco¹

• ¹Department Biological Sciences, Faculty of Science, University of Cape Town, Cape Town, Western Cape, South Africa
• ²Department of Biology, Faculty of Science, York University, Toronto, Ontario, Canada
• ³Department of Chemistry, Faculty of Science, University of Cape Town, Cape Town, Western Cape, South Africa

The study deals with cloning and deorphanizing a GPCR receptor of the stick insect, Carausius morosus, as a true adipokinetic (AKH)/hypertrehalosemic (HrTH) receptor involved in metabolic activity. It is activated by the endogenous hypertrehalosemic decapeptides of the stick insect when stably expressed in a mammalian cell culture system. Structure-activity studies where each of the ten amino acids of the endogenous peptide is successively replaced by a simple Ala residue give insight into the importance of the termini of the ligand and the side chains of the individual amino acids. Essential for receptor activation are the blocked N-terminus (pGlu), C-terminus (carboxyamide), Phe at position 4, Trp at position 8, Thr at positions 3 and 5. A medium reduction in efficacy (5 to 10 fold) was measured when positions 2, 6, 7 or 9 were substituted by Ala, whereas replacement of Thr at position 10 had no deleterious effect. Chain length was important: a nona-or octapeptide with otherwise exactly the same sequence as the native peptide activated the receptor 5 to 10 fold less. These data will be used in future in combination with NMR measurements of the ligand and dynamic modelling to understand how the HrTH ligand behaves in the binding pocket of the receptor and how non peptide mimetics can be manufactured to find super agonists or antagonists for possible use to combat these potential pest insects.