1. Full sequence and characterization of two insect defensins: immune peptides from the mosquito Aedes aegypti
R Chalk, C M Albuquerque, P J Ham, H Townson Proc Biol Sci. 1995 Aug 22;261(1361):217-21. doi: 10.1098/rspb.1995.0139.
We report the complete amino acid sequence and biological activity of two immune peptides, from the yellow fever mosquito Aedes aegypti, that are induced in response to infection. Both peptides display biological activity against the Gram positive microbe Micrococcus luteus and substantial sequence homology to insect defensins, small heat-stable, antibiotic peptides previously described from several non-vector insects. These mosquito peptides, designated Ae. aegypti defensins A and B, are isoforms. Defensin B is the most abundant antibacterial peptide in this species whereas defensin A is much less abundant and carries two amino acid substitutions compared to defensin B, making it more basic in character. Apparent convergence between isoforms from Ae. aegypti and the fleshfly Phormia terranovae is discussed. The synergistic activity previously described between Ae. aegypti immune haemolymph and lysozyme is not caused by these peptides because synergy occurred only at concentrations far outside the physiological range seen in Ae. aegypti.
2. Cloning and characterization of cDNAs encoding the antibacterial peptide, defensin A, from the mosquito, Aedes aegypti
W L Cho, Y C Fu, C C Chen, C M Ho Insect Biochem Mol Biol. 1996 Apr;26(4):395-402. doi: 10.1016/0965-1748(95)00108-5.
Insect defensins are cationic, inducible antibacterial peptides. Four full-length cDNAs encoding defensin A from the mosquito Aedes aegypti were cloned using polymerase chain reaction (PCR) and sequenced. All four cDNAs are 473 base pairs long, bearing an open reading frame of 98 amino acids with a few substitutions in the signal peptide domain. The deduced amino acid sequence of Aedes aegypti defensin (AaDef) contains a signal peptide sequence of 18 amino acids followed by a 40-amino acid putative propeptide domain and a 40-amino acid mature peptide domain. The mature peptide, with a predicted M(r) of 4148, shows 80% identity and 93% similarity to Phormia defensin A, and is identical to the peptide sequencing data for mosquito defensin A of Lowenberger et al. (1995) and B of Chalk et al. (1995). There are three potential phosphorylation sites but no glycosylation sites detected in AaDef. Three putative disulfide linkages between cysteines, characteristic of insect defensins, are conserved in AaDef. Aedes aegypti defensin mRNA is produced in response to a bacterial challenge; it is dramatically enhanced 6 h after bacterial injection, continues to increase through 24 h, and is maintained at high levels until at least 30 h post-bacterial injection.
3. Insect immunity: isolation from immune blood of the dipteran Phormia terranovae of two insect antibacterial peptides with sequence homology to rabbit lung macrophage bactericidal peptides
J Lambert, E Keppi, J L Dimarcq, C Wicker, J M Reichhart, B Dunbar, P Lepage, A Van Dorsselaer, J Hoffmann, J Fothergill Proc Natl Acad Sci U S A. 1989 Jan;86(1):262-6. doi: 10.1073/pnas.86.1.262.
We have isolated from the hemolymph of immunized larvae of the dipteran insect Phormia terranovae two peptides that are selectively active against Gram-positive bacteria. They are positively charged peptides of 40 residues containing three intramolecular disulfide bridges and differ from one another by only a single amino acid. These peptides are neither functionally nor structurally related to any known insect immune response peptides but show significant homology to microbicidal cationic peptides from mammalian granulocytes (defensins). We propose the name "insect defensins" for these insect antibiotic peptides.
