Peptidoglycan recognition protein 6 (PGRP6) from Asian corn borer, Ostrinia furnacalis (Guenée) serve as a pattern recognition receptor in innate immune response.

Peptidoglycan recognition proteins (PGRPs) recognize invading microbes via detecting peptidoglycans from microbial cell walls. PGRPs are highly conserved from insects to vertebrates and all play roles during the immune defensive response. Ten putative PGRPs have been identified through transcriptome analysis in the Asian corn borer, Ostrinia furnacalis (Guenée). Whereas, the biochemical functions of most of them have not yet been elucidated. In this study, we found PGRP6 messenger RNA exhibited extremely high expression levels in the midgut, and its transcript level increased dramatically upon bacterial infection. Moreover, the enzyme-linked immunosorbent assay indicated recombinant PGRP6 exhibited a strong binding affinity to peptidoglycans from Micrococcus luteus and Bacillus subtilis, which could agglutinate M. luteus and yeast Pichia pastoris. Additionally, we demonstrated that PGRP6 was involved in the pathway of antimicrobial peptides synthesis, but could not enhance encapsulation and melanization of hemocytes. Overall, our results indicated that O. furnacalis PGRP6 serves as a pattern recognition receptor and detects peptidoglycans from microbes to initiate the immune response.

Peptidoglycan recognition protein-S1 (PGRP-S1) from Diaphania pyloalis (Walker) is involved in the agglutination and prophenoloxidase activation pathway.

Recognition of invading foreign exogenous pathogen is the first step to initiate the innate immune response of insects, which accomplished by the pattern recognition receptors (PRRs). Peptidoglycan recognition proteins (PGRPs) serve as an important type of PRRs, which activate immune response by detecting peptidoglycan of microbial cell wall. In this study, we have cloned the full-length cDNA of PGRP gene called PGRP-S1 from the Diaphania pyloalis (Walker). The open reading frame (ORF) of D. pyloalis PGRP-S1 encodes 211 amino acids which containing a secretion signal peptide and a canonical PGRP domain. Multisequence alignment revealed that PGRP-S1 possess the amino acid residues responsible for zinc binding and amidase activity. D. pyloalis PGRP-S1 exhibited the highest transcript level in fat body and followed in head. The mRNA concentration dramatically increased after an injection of Escherichia coli or Micrococcus luteus. Purified recombinant PGRP-S1 exhibit binding ability to peptidoglycans from Staphylococcus aureus or Bacillus subtilis and cause intensive agglutination of E. coli, M. luteus or S. aureus in the presence of zinc ions. Furthermore, phenoloxidase activity significantly increased when the plasma from larvae was incubated with recombinant PGPR-S1 and peptidoglycans from B. subtilis or M. luteus simultaneously. These results implied that PGRP-S1 was a member involving the prophenoloxidase activation pathway. Overall, our results indicated that D. pyloalis PGRP-S1 serve as a PRR to participate in the recognition of foreign pathogen and prophenoloxidase pathway stimulation.