Structure and function of the coleoptericin gene in the ladybird beetle Serangium japonicum during seasonal development

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OBJECTIVE: This study was conducted to explain the relationship between structure and function of coleoptericin in Serangium japonicum, and importance of the differential expression patterns of it between in winter and summer, and to provide a theoretical foundation for the rational application of S. japonicum as a natural enemy in pest control. METHOD: The full length cDNA was obtained using rapid amplification of cDNA ends (RACE) technology. Bioinformatics software was employed to predict the structure and physicochemical properties of the coleoptericin protein based on its cDNA sequence. The prokaryotic expression protein were tested activity of anti against three experimental strains of microorganisms through using the pore diffusion method. Additionally, metagenome was sequenced and analyzed to find the proteins' effect on microorganism in S.japonicum. RESULT: The full-length cDNA sequence of coleoptericin was found to be 606 base pairs (bp) in length. Its open reading frame (ORF) spanned from nucleotide 48 to 495, totaling 447 bp, and encoded a polypeptide of 149 amino acids. Homology analysis revealed that the deduced amino acid sequence shared the highest similarity (55.1%) with the antimicrobial peptide from Tribolium castaneum. The protein had molecular weight of 17.03 kD and theoretical i-soelectric point of 9.19. Hydrophilicity analysis indicated a grand average of hydropathicity (GRAVY) score of -0.85, suggesting a hydrophilic nature. Furthermore, the protein was predicted to contain one transmembrane domain and a signal peptide. Agar well diffusion assays demonstrated that the prokaryotically expressed coleoptericin exhibited antimicrobial activity against Escherichia coli. Results from Metagenome showed that the abundance of Penicillium was significantly lower in winter compared to summer. CONCLUSION: The coleoptericin protein from S.japonicum had a sequence of over 100 amino acid residues and an α-helical secondary structure. For S. japonicum, our results supported that coleoptericin protein could protect the beetle from pathogenic bacteria in winter. Some results from relative reports suggested that coleoptericin protein also could be an antifreeze energy source except for immune function.

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