Two isoforms of a member of the arthropod defensin family from the soft tick, Ornithodoros moubata (Acari: Argasidae)

We previously purified and determined the partial amino acid sequence of a 4 kDa peptide having high homology with scorpion defensin from the hemolymph of adult fed female soft ticks, Ornithodoros moubata. In this study, the full length sequences of two defensin isoforms were obtained. Deduced amino acid sequences reveal a precursor protein of 73 amino acid residues with a mature portion consisting of 37 amino acid residues. This mature peptide contains six cysteine residues conserved in the same location as other invertebrate defensins. Phylogenetic analysis reveals that Ornithodoros defensin is most closely related to scorpion defensin and other more ancient arthropods. Ornithodoros defensin mRNA is constitutively expressed and up-regulated by blood-feeding and bacterial injection. Ornithodoros defensin gene expression occurs mainly in the midgut. This is the first report of the cloning and gene expression of an antibacterial peptide from the Acari.