Cloning and characterization of cDNAs encoding the antibacterial peptide, defensin A, from the mosquito, Aedes...

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.