title: Effects of Manduca sexta allatostatin and an analog on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut.
abstract: The C-type allatostatin, Manduca sexta allatostatin (Manse-AS) and the analog delta R(3)delta R(5)Manse-AS, where R residues were replaced by their d-isomers, were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Both peptides had significant dose-dependent feeding suppression effects, resulting in mortality, reduced growth and fecundity compared with control insects. The delta R(3)delta R(5)Manse-AS analog had an estimated LC(50) of 0.18 microg/microl diet, and was more potent than Manse-AS. At a dose of 0.35 microg delta R(3)delta R(5)Manse-AS/microl diet, 98% of aphids were dead within 3 days, at a rate similar to those aphids that had been starved (no diet controls). On comparison, it required 13 days and three times the dose of Manse-AS fed to aphids to attain 96% mortality. It is possible that the feeding suppression effects of Manse-AS on aphids are due to the inhibition of gut motility. The estimated half-life of Manse-AS when incubated with a gut extract from A. pisum was 54 min. Degradation was most likely due to cathepsin L cysteine and/or trypsin-like proteases, by an unidentified glutamine-specific protease and by a carboxypeptidase-like enzyme. The d-isomers of R in the Manse-AS analog appeared to prevent hydrolysis by cathepsin L cysteine and trypsin-like enzymes, and enhance its half-life (145 min). However delta R(3)delta R(5)Manse-AS was cleaved by enzymes with carboxypeptidase-like and chymotrypsin-like activity. The increased stability of the Manse-AS analog may explain its enhanced feeding suppression effects when continually fed to aphids, and demonstrates the potential use of Manse-AS in a strategy to control aphid pests.
authors: The Food and Environment Research Agency, Sand Hutton, York YO41 1LZ, UK. rachel.down@fera.gsi.gov.uk
authors: Rachel E
authors: RE
authors: Down
authors: H June
authors: HJ
authors: Matthews
authors: Neil
authors: N
authors: Audsley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids / Q000187:drug effects* / Q000378:metabolism*; D002268:Carboxypeptidases / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002918:Chymotrypsin / Q000378:metabolism; D057056:Cysteine Proteases / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000201:enzymology*; D019476:Insect Proteins / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D010455:Peptides; C071432:allatostatin protein, Manduca sexta; D002268:Carboxypeptidases; D057056:Cysteine Proteases; D002918:Chymotrypsin; D014357:Trypsin