Infection-induced molecular pattern recognition proteins in larvae of Protaetia brevitarsis seulensis (Coleoptera: Cetoniidae)

We cloned and sequenced full-length peptidoglycan recognition protein (PGRP)-like cDNAs, named PS PGRP-SA(a)-like, PS PGRP-SA(b)-like, PS PGRP-SB1-like and PS PGRP-SC-like, from Protaetia brevitarsis seulensis. The amino acid sequences of PS PGRPs share 32.03-47.93% homology with those of PGRP family members in insects and mammals, including humans. We identified a conserved consensus sequence for amidase activity (His; H-Tyr; Y-His; H-Thr; T-Cys; C) and residues for binding peptidoglycan (PGN), one of the major bacterial cell wall components, including Asp (D) and Phe (F) for Lys-type PGN; and Gly(G), Trp (W) and Arg (R) for DAP-type PGN. The topological structures of PS PGRP-SA(a)-like, PS PGRP-SA(b)-like and PS PGRP-SC-like proteins are structurally similar to those of Drosophila melanogaster PGRP-SA, which has three α-helices and six β-strands. The β-strands are located in a central region and helix α1 on the back and peripheral α2 and α3 helices are on the front. The three α-helices and six β-strands are also present in PS PGRP-SB1-like, but the topological structure differs from that of typical PGRP. Significantly increased levels of PS PGRP-SA (a)-like and PS PGRP-SA (b)-like mRNA were recorded when Gram-positive bacteria or yeast cells were injected into larvae. PS PGRP-SB1-like mRNA levels were up-regulated by infection by all three pathogens; however, expression of PS PGRP-SC-like mRNA was increased 20- or 30-fold only shortly after injection with Gram-negative bacteria.