Novel attacin from Hermetia illucens: cDNA cloning, characterization, and antibacterial properties

In this study, we report a novel member of the attacin family from Hermetia illucens. The cDNA clone encoding the attacin-like protein was isolated by screening a cDNA library prepared from immunized fat body. The complete 510 bp cDNA of HI-attacin was predicted to encode a protein of 169 amino acids with a molecular weight of 17.7 kDa. The putative mature protein of H. illucens attacin (HI-attacin) had 50% identity with that of Bactrocera dorsalis attacin B. Phylogenetic analysis revealed that the HI-attacin was separated from the other dipteran attacins with a high bootstrap percentage. Compared to that in the other dipteran attacins, the G1 domain of HI-attacin was shorter and the sequence of the G2 domain of HI-attacin was more conserved than that of the G1 domain. We produced the recombinant attacin (rHI-attacin) protein using a prokaryotic expression system to confirm its antibacterial character. The rHI-attacin was produced as inclusion bodies and refolded by on-column refolding. rHI-attacin exhibited antibacterial activity against both Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA). Using real-time PCR, the expression of HI-attacin was was barely detected before the immunization, but was mostly evident in the fat body after immunization.