Ecdysis triggering hormone peptide in the African malaria mosquito Anopheles gambiae: The peptide structure for receptor activation.

Infections by mosquito-borne diseases represent one of the leading causes of death in third world countries. The rapid progression of resistance to conventional insecticide causes a significant threat to the highly efficient preventive methods currently in place. Insect neuropeptidergic system offers potential targets to control the insect vectors. The essential roles of the neuropeptide ecdysis triggering hormone (ETH) in insect development and reproduction led us to attempt understanding of the fundamentals of the biochemical interaction between ETH and its receptor in the African malaria mosquito Anopheles gambiae. One of two ETH peptides of the African malaria mosquito (AgETH1), a small peptide hormone with 17 amino acid residues (SESPGFFIKLSKSVPRI-NH2 ), was studied to elucidate its molecular structure. N-termini deletions and mutations of conserved amino acids in the ligand revealed the critical residues for the receptor activation. The solution structure of AgETH1 using 2D 1 H-1 H nuclear magnetic resonance (NMR) spectroscopy and nuclear overhauser effect (NOE) derived constraints revealed a short alpha helix between residues 3S and 11S. The NMR solution structure of AgETH1 will be of significant assistance for designing a new class of insecticidal compounds that acts on the AgETH receptor aiming for in silico docking studies.

Expression and Characterization of Manduca sexta Stress Responsive Peptide-1; an Inducer of Antimicrobial Peptide Synthesis.

In response to stress conditions such as wounding or infections in insects, several short peptides are processed to act as cytokines that induce AMP gene expression. To study their structure-activity relationship, immune inducibility, tissue specificity, stress responsiveness, and development relatedness, we chemically synthesized Manduca sexta stress response peptide-1, a 25-residue peptide with one disulfide bond (SRP1: FGVRVGTCPSGYVRRGTFCFPDDDY). Upon injection of the SRP1 into naïve larvae, several antimicrobial peptide genes were expressed at higher levels. The mRNA levels of SRP1 increased significantly in hemocytes and fat body after larvae were challenged with a mixture of bacteria and ß-1,3-glucan. The expression patterns of SRP1 and its target genes are somewhat different from SRP2's, suggesting overlapping yet distinct functions. We elucidated the 3D structure of SRP1 in solution by two-dimensional 1H-1H NMR spectroscopy. The tertiary structure of SRP1 consists of two short ß-strands at Y12-R15 and F18-F20, one type-II ß-turn at R15-F18 in its well-defined core and is stabilized by a covalent disulfide bond between C8 and C19. The conformational ensemble of SRP1 from extensive atomistic simulation in explicit solvent (with 3.0 µs total effective sampling) shows high consistency with experimental intramolecular NOEs of the core region. The SRP1 core adopts a fold similar to the carboxyl-terminal subdomain of epidermal growth factor (EGF), suggesting that SRP1 may interact with EGF receptor-like molecules to trigger its biological function.