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Functional characterization of short-type peptidoglycan recognition proteins (PGRPs) from silkworm Bombyx mori in
Ruo-Nan Zhang1, Cai-Ting Li1, Fei-Fei Ren1
1Laboratory of Insect Molecular Biology and Biotechnology, Guangdong Provincial Key Laboratory of Agro-animal Genomics and Molecular Breeding, College of Animal Science, South China Agricultural University, Guangzhou, 510642, China.
Abstract:
Peptidoglycan recognition proteins (PGRPs) are members of an important class of pattern recognition receptors in insects that can specifically recognize peptidoglycan (PGN) in bacterial cell walls and participate in immune regulation and bacterial clearance. Although the role of PGRPs in regulating the innate immune response in Drosophila melanogaster has been studied, little is known regarding PGRPs in Lepidoptera species. In this study, five short (S)-type Bombyx mori PGRPs (BmPGRPs) were cloned, expressed, and evaluated for their function in innate immunity. B. mori larvae that were injected with the gram-positive bacterium Bacillus megaterium or the gram-negative bacterium Escherichia coli exhibited a rapid and significant upregulation in S-type BmPGRP expression. The results showed that the five evaluated BmPGRPs have significant agglutination activity toward E. coli and B. megaterium and more notable amidase activity toward meso-diaminopimelic acid peptidoglycan (DAP-PGN). Furthermore, only in the presence of BmPGRP-S5 did B. mori larval hemocytes exhibit significant phagocytosis against E. coli and B. megaterium.
Insights
This study reveals that five short Bombyx mori peptidoglycan recognition proteins (BmPGRPs) show significant immune activity. These BmPGRPs exhibit agglutination and amidase functions, with BmPGRP-S5 enhancing phagocytosis in silkworm larvae.
Area of Science:
- Insect immunology
- Biochemistry
- Molecular biology
Background:
- Peptidoglycan recognition proteins (PGRPs) are crucial pattern recognition receptors in insects, essential for recognizing bacterial peptidoglycan and mediating innate immunity.
- While studied in Drosophila melanogaster, the functions of PGRPs in Lepidoptera species, like the silkworm Bombyx mori, remain largely unexplored.
Purpose of the Study:
- To clone, express, and functionally characterize five short (S)-type Bombyx mori PGRPs (BmPGRPs) in the context of innate immunity.
- To investigate the role of these BmPGRPs in immune responses against bacterial infections in B. mori larvae.
Main Methods:
- Cloning and expression of five S-type BmPGRP genes.
- Analysis of BmPGRP expression levels in B. mori larvae following bacterial challenge (Bacillus megaterium and Escherichia coli).
- In vitro assessment of BmPGRP agglutination and amidase activities against specific bacterial species and peptidoglycan types.
- Evaluation of BmPGRP-mediated phagocytosis by B. mori hemocytes.
Main Results:
- S-type BmPGRP expression was significantly upregulated in B. mori larvae challenged with B. megaterium or E. coli.
- The five evaluated BmPGRPs demonstrated significant agglutination activity against both E. coli and B. megaterium.
- BmPGRPs exhibited notable amidase activity, particularly against meso-diaminopimelic acid peptidoglycan (DAP-PGN).
- BmPGRP-S5 was identified as a key mediator, significantly enhancing hemocyte phagocytosis against E. coli and B. megaterium.
Conclusions:
- The study identifies and characterizes five S-type BmPGRPs with diverse innate immune functions in Bombyx mori.
- These BmPGRPs play roles in bacterial recognition, clearance, and immune regulation, contributing to the silkworm's defense mechanisms.
- BmPGRP-S5 emerges as a critical component in promoting phagocytosis, highlighting its importance in insect immunity.
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