Acta Entomologica Sinica ›› 2020, Vol. 63 ›› Issue (11): 1333-1344.doi: 10.16380/j.kcxb.2020.11.006

• RESEARCH PAPERS • Previous Articles     Next Articles

Antibacterial activity of BmPGRP-S5 of Bombyx mori and its role in cellular immunity 

CHEN Xue1, ZHOU Hong1, LI Xiao-Feng1, XIAO Yang2, ZHONG Yang-Jin1, YANG Wan-Ying1,*   

  1.  (1. Guangdong Provincial Key Laboratory of Agroanimal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou 510642, China; 2. Institute of Sericulture and Processing of Agricultural Products, Guangdong Academy of Agricultural Sciences, Guangzhou 510610, China)
  • Online:2020-11-20 Published:2020-12-08

Abstract: 【Aim】 Peptidoglycan-recognition proteins (PGRP) can specifically recognize peptidoglycan (PGN) in bacterial cell walls, and trigger the production of antimicrobial peptides through the immune deficiency (IMD) pathway and Toll pathway in insects. This study aims to explore the antibacterial activity of the Bombyx mori PGRP-S5 (BmPGRP-S5) and its function in initiating the cellular immunity in B. mori. 【Methods】 BmPGRP-S5 protein was expressed in Drosophila embryonic S2 cell line. The antibacterial activities of BmPGRP-S5 protein to Escherichia coli K12D31, Staphylococcus aureus and Bacillus megaterium were assayed based on the bacterial growth curve. The binding ability of BmPGRP-S5 protein to bacterial cell wall components of E. coli, S. aureus and Bacillus subtilis was detected by ELISA. The effect of BmPGRP-S5 on the activation of prophenoloxidase (PPO) by bacterial cell wall components was analyzed by measuring the absorbance value and observing the hemolymph melanization reaction of B. mori. The effect of BmPGRP-S5 on the 
phagocytosis to bacteria by B. mori hemocytes was detected by fluorescein isothiocyanate isomer (FITC) labeling method. 【Results】 The expressed and purified BmPGRP-S5 protein was obtained. BmPGRP-S5 had no antibacterial effect on S. aureus, E. coli K12D31 and B. megaterium. However, after adding 40 μmol/L Zn2+, the antibacterial effect of BmPGRP-S5 protein on B. megaterium was significantly enhanced. The ELISA results showed that the binding ability of BmPGRP-S5 with PGN from S. aureus and lipoteichoic acid (LTA) from B. subtilis was strong, which also promoted the activation of phenoloxidase in B. mori hemolymph by these two bacterial cell wall components. The melanization reaction of B. mori hemolymph mediated by cell wall components was accelerated by BmPGRP-S5. After adding BmPGRP-S5 protein, the phagocytic rates of B. mori hemocytes to S. aureus, E. coli K12D31 and B. megaterium increased to about 53.33%, 25.83%, and 30.83%, respectively, which were significantly higher than those of the control groups. 【Conclusion】 The antibacterial activity of BmPGRP-S5 is dependent on Zn2+ and may be related to its amidase activity. BmPGRP-S5 can play a role in melanization and phagocytosis in B. mori by recognizing bacterial cell wall components PGN or LTA. The BmPGRP-S5 protein used in this study was obtained by the recombinant expression in Drosophila S2 cells and can more truly display its functional activity in the physiological state of insects. Therefore, the results are instructive for the further development and utilization of BmPGRP-S5.

Key words: Bombyx mori, BmPGRP-S5 protein, melanization reaction, cell phagocytosis; antibacterial activity