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A single-CRD C-type lectin is important for bacterial clearance in the silkworm
Ming-Yue Zhan1, Toufeeq Shahzad1, Pei-Jin Yang1
1School of Plant Protection, Anhui Agricultural University, Hefei, Anhui 230036, China.
Insights
The silkmoth C-type lectin-S3 (CTL-S3) protein enhances insect immunity by binding bacterial components. This lectin promotes pathogen clearance in larvae, acting as an opsonin to boost immune responses against bacterial infections.
Area of Science:
- Insect immunology
- Molecular biology
- Biochemistry
Background:
- C-type lectins (CTLs) utilize a calcium-dependent carbohydrate-recognition domain (CRD) for carbohydrate binding, playing vital roles in animal immunity.
- While dual-CRD CTLs (immulectins) in lepidopterans are known pathogen recognizers, the functions of single-CRD CTLs in insects remain largely unexplored.
- This study focuses on characterizing a single-CRD CTL from the silkmoth Bombyx mori.
Purpose of the Study:
- To characterize the immune-related functions of a single-CRD CTL, named CTL-S3, from the silkmoth Bombyx mori.
- To investigate the expression, localization, and functional activity of CTL-S3 in response to bacterial challenges.
Main Methods:
- Gene cloning and sequencing of CTL-S3 from Bombyx mori.
- Quantitative analysis of CTL-S3 mRNA expression in various tissues and after bacterial challenge.
- Detection of CTL-S3 protein secretion into larval hemolymph.
- Biochemical assays using recombinant CTL-S3 (rCTL-S3) to assess binding to bacterial components and its effects on bacterial growth and agglutination.
- In vivo experiments to evaluate the role of CTL-S3 in pathogen clearance from larvae.
Main Results:
- The CTL-S3 gene comprises a 672 bp open reading frame encoding a 223-amino acid protein.
- CTL-S3 gene expression was upregulated in fertilized eggs and larvae following bacterial infection.
- CTL-S3 protein was detected in the larval hemolymph.
- Recombinant CTL-S3 (rCTL-S3) demonstrated binding to bacterial cell wall components and whole bacteria.
- CTL-S3 exhibited antibacterial activity by inhibiting Bacillus subtilis growth and causing Staphylococcus aureus agglutination.
- Administration of CTL-S3 significantly accelerated the clearance of Escherichia coli and Staphylococcus aureus from the hemolymph of larvae.
Conclusions:
- CTL-S3 is a secreted single-CRD C-type lectin in Bombyx mori with significant roles in innate immunity.
- CTL-S3 functions as an opsonin, enhancing the phagocytic or clearance mechanisms against bacterial pathogens in the hemolymph.
- These findings contribute to understanding the immune defense mechanisms mediated by CTLs in insects.
Abstract:
C-type lectins (CTLs) depend on the carbohydrate-recognition domain (CRD) to recognize carbohydrates by a Ca(2+)-dependent mechanism. In animals, CTLs play critical roles in pathogen recognition, activation of the complement system and signaling pathways. Immulectins (Dual-CRD CTLs) in lepidopteran are involved in recognizing pathogens. However, little is known about the immune-related functions of insect single-CRD CTLs. Here, we reported the characterization of C-type lectin-S3 (CTL-S3), a single-CRD CTL from the domesticated silkmoth Bombyx mori (Lepidoptera: Bombycidae). The ORF of CTL-S3 gene is 672 bp, which encodes a putative protein of 223 amino acids. CTL-S3 gene was expressed in a variety of tissues. Levels of CTL-S3 mRNA in fertilized eggs and whole larvae were elevated upon bacterial challenges. CTL-S3 was secreted to larval hemolymph. The recombinant protein (rCTL-S3) binds to bacterial cell wall components and bacteria. CTL-S3 inhibited the growth of Bacillus subtilis and caused agglutination of Staphylococcus aureus. More importantly, CTL-S3 facilitated the rapid clearance of Escherichia coli and Staphylococcus aureus from the body cavity of larvae. Taken together, our results suggested that CTL-S3 may function as an opsonin in larval hemolymph to enhance the clearance of pathogens.
