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Peptidoglycan recognition protein-S5 functions as a negative regulator of the antimicrobial peptide pathway in the

Kangkang Chen1, Lin Zhou1, Feng Chen1

  • 1Department of Entomology, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi 712100, China.

Developmental and Comparative Immunology
|March 26, 2016
PubMed

Insights

Silkworm PGRP-S5

Area of Science:

  • Insect immunology
  • Molecular biology
  • Biochemistry

Background:

  • The proPO, IMD, and Toll pathways are key to insect immunity, controlling melanization and antimicrobial peptide production.
  • Peptidoglycan recognition proteins (PGRPs) function as receptors and regulators in these pathways, with some possessing antimicrobial properties.
  • Silkworm PGRP-S5 was previously shown to recognize peptidoglycans (PGs), activate the proPO pathway, and exhibit bactericidal activity via amidase function.

Purpose of the Study:

  • To investigate the role of PGRP-S5's amidase activity in its immune functions.
  • To elucidate the mechanism by which PGRP-S5 regulates the proPO and IMD pathways.
  • To understand the multifaceted role of PGRP-S5 in the silkworm humoral immune system.

Main Methods:

  • Site-directed mutagenesis was used to generate a C177S mutant of silkworm PGRP-S5, abolishing amidase activity while preserving PG-binding.
  • Functional assays were performed to assess the mutant protein's ability to activate the proPO pathway and regulate antimicrobial peptide generation.
  • The role of amidase activity in PGRP-S5's interaction with the IMD pathway was examined.

Main Results:

  • The C177S mutation rendered PGRP-S5 incapable of activating the proPO pathway, indicating PG processing is essential for initiating the complex.
  • PGRP-S5 was found to negatively regulate antimicrobial peptide generation in an amidase-dependent manner, likely involving the IMD pathway.
  • These findings highlight the necessity of amidase activity for PGRP-S5's receptor function in proPO activation and its modulatory role in antimicrobial peptide production.

Conclusions:

  • Silkworm PGRP-S5's amidase activity is crucial for its function in activating the proPO pathway.
  • PGRP-S5 acts as a negative regulator of antimicrobial peptide production through an amidase-dependent mechanism, likely via the IMD pathway.
  • Silkworm PGRP-S5 functions as a versatile immune component, acting as a sensor, modulator, and effector in the humoral immune response.
Keywords:
Antimicrobial peptideBombyx moriImmunePeptidoglycan recognition proteinsProphenoloxidase

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