Identification and characterization of two peptidoglycan recognition proteins with zinc-dependent antibacterial activity from the cotton bollworm, Helicoverpa armigera

Peptidoglycan recognition proteins (PGRPs) specifically bind to peptidoglycan and play an important role in the innate immune responses as pattern recognition receptors (PRRs). Here we identified and characterized two PGRPs (HaPGRP-B and HaPGRP-C) from the cotton bollworm, Helicoverpa armigera. The comparative analysis indicated that five amino acids which are required for T7 lysozyme Zn2+ binding and amidase activity are conserved in HaPGRP-B and HaPGRP-C, suggesting that the two PGRPs are members of the amidase-type PGRPs. HaPGRP-B and HaPGRP-C mRNA increased in both the fat bodies and the hemocytes after an injection of Gram-negative Escherichia coli or Gram-positive Staphylococcus aureus. Recombinant HaPGRP-B and HaPGRP-C could agglutinate E. coli and S. aureus in a zinc-dependent manner. More importantly, both rHaPGRP-B and rHaPGRP strongly inhibited the growth of E. coli and S. aureus in the presence of Zn2+. Moreover, the HaPGRP-B mRNA showed up-regulation post hormones (20E and methoprene) injection. Our results indicate that the two PGRPs of H. armigera may play an important role in defending against bacteria as amidase-type PGRPs and the hormones can function in regulating the expressions of PGRPs.

► Two PGRP genes were identified from Helicoverpa armigera.
► The expression of HaPGRPs was up-regulated after an injection of bacteria.
► Recombinant HaPGRPs could agglutinate bacteria in a zinc-dependent manner.
► Recombinant HaPGRPs strongly inhibited the growth of bacteria in the presence of Zn2+.
► Hormones could regulate the expression of HaPGRP-B.