Identification and expression analysis of antibacterial peptides from venom of the scorpion Mesobuthus martensii

As one kind of important component of animal innate immune system, many antibacterial peptides (ABPs) have been characterized from scorpion venoms. However, the genomic organization and structure of the genes encoding these venom-derived peptides have been rarely reported yet. It still remains unclear whether these ABPs are essential to the immune protection of scorpion venom glands and most of them could not be confirmed at the protein level. The scorpion Mesobuthus martensii (M. martensii) is an important raw material in Chinese Traditional Medicine for the treatment of some nervous system diseases.

Here, we tried to identify three ABPs (BmKb1, BmKn2 and BmKbpp) from the venom of M. martensii at the genomic, transcriptional and protein levels. We have cloned the genomic sequences encoding these three ABPs by analyzing the draft genome of M. martensii decoded previously by our group. Two of these ABP genes share the same genomic organization and structure of two exons and one intron with the GT-AG splice junction located in the DNA region encoding the N-terminal part of signal peptide. To further explore molecular mechanism of scorpion venom gland immunity, a modified method was applied to establish an infection model. Using this model, two genes (BmKb1 and BmKn2) were revealed to have a significant up-regulation at the transcriptional level after challenged by Staphylococcus aureus or Escherichia coli. This is even more strengthened by the presence of several immune response elements locating at their corresponding promoter regions. Finally, we also putatively identified the existence of these three ABPs in the natural venom of M. martensii.

Thus, our work gained insight into the genomic organization and diversity of ABPs from scorpion and provides evidence supporting the key defense role of venom-derived ABPs in controlling scorpion venom gland infection.