Identification and characterization of the parasitic wasp Nasonia defensins: Positive selection targeting the functional region?

• Published in: Developmental and comparative immunology 2010-06, Vol.34 (6), p.659-668
• Main Authors: Gao, Bin, Zhu, Shunyi
• Format: Article
• Language: English
• Subjects: Adaptive evolution; Amino Acid Sequence; Animals; Apis mellifera; Cloning, Molecular; Defensins - genetics; Defensins - immunology; Defensins - metabolism; Escherichia coli; Evolution, Molecular; Gene Duplication; Gene Expression Regulation, Developmental; Gram-Positive Bacteria - growth & development; Gram-Positive Bacteria - immunology; Gram-Positive Bacteria - pathogenicity; Gram-Positive Bacterial Infections - genetics; Gram-Positive Bacterial Infections - immunology; Gram-Positive Bacterial Infections - metabolism; Hymenoptera; Immunity, Innate; Innate immunity; Insect Proteins - genetics; Insect Proteins - immunology; Insect Proteins - metabolism; Life Cycle Stages - genetics; Life Cycle Stages - immunology; Molecular Sequence Data; Musca domestica; Nasonia; Parasitoid; Phylogeny; Pteromalidae; Recombinant peptide; Recombinant Proteins - genetics; Recombinant Proteins - immunology; Recombinant Proteins - metabolism; Wasps - immunology; Wasps - microbiology
• ISSN: 0145-305X; 1879-0089
• DOI: 10.1016/j.dci.2010.01.012

Defensin is a crucial component of innate immunity highly conserved across different insect orders. Here, we report identification and characterization of defensins in the parasitic wasp Nasonia (Hymenoptera: Pteromalidae). In comparison with those in the non-parasitic insect Apis mellifera, two different subtypes of defensins (defensin1 and defensin2) have undergone independent gene duplication to create a mutigene family of five members (named 1-1, 1-2, 2-1, 2-2 and 2-3) in the Nasonia lineage. Such duplication occurred before the divergence of three sibling species ( N. vitripennis, N. giraulti and N. longicornis) and the duplicated genes was subsequently subjected to positive selection at the amino-terminal loop and the γ-core region. RT-PCR identified that only the subtype 1 of defensins were constitutively expressed in the N. vitripennis adult stage and none of the five defensins was expressed in other developmental stages (i.e. the infected Musca domestica pupae). A functional form of 2-2 in N. vitripennis (named navidefensin2-2) was produced in Escherichia coli by an on-column refolding approach. The recombinant peptide presented a typical defensin structure, as identified by CD analysis, and selectively inhibited the growth of two Gram + bacteria at low micromolar concentrations. The bioactive surface responsible for antibacterial activity of navidefensin2-2 was identified in the γ-core region of this molecule. Positive selection targeting the antibacterial region of defensins could be a consequence of evolutionary arms race between Nasonia and its pathogens.