In silico identification, structural characterization, and phylogenetic analysis of MdesDEF-2: a novel defensin from the Hessian fly, Mayetiola destructor.

The CSαβ defensins are one of the most ancient antimicrobial peptide classes and are distributed in plants, invertebrates, and fungi. In the insect immunity, the defensins play a crucial role in protection against pathogens. The discovery of novel insect defensins could be a vital tool in developing novel antimicrobial agents, which are urgently needed because of growing resistance in pathogenic bacteria and the resulting reduction in the effectiveness of conventional antibiotics over the years. In this context, novel insect defensins could be identified from the potential resource of model insects. Here, a novel defensin, MdesDEF-2, was identified from the model insect Mayetiola destructor, the most destructive insect pest of wheat worldwide. The in silico identification of MdesDEF-2 was done through searching by regular expression in M. destructor's protein sequences available at NCBI. MdesDEF-2 has 36 amino acid residues and its model was composed of two β-strands and one α-helix showing three disulfide bridges. According to the classification of CSαβ defensins, MdesDEF-2 belongs to the group of ancient insect-type defensins. The molecular dynamics simulation revealed that MdesDEF-2 has a very flexible N-terminal loop. Moreover, phylogenetic analysis together with functional predictions indicated that MdesDEF-2 could have antibacterial activity without causing membrane disruption. However, while the actual activity of MdesDEF-2 is still unclear, it is evident that its role in the biology of M. destructor is similar to that of its paralogue, MdesDEF-1, protecting the insect against microbial invasion.