A Scavenger Function for a DrosophilaPeptidoglycan Recognition Protein

Abstract

Recent studies of peptidoglycan recognition protein (PGRP) have shown that 2 of the 13 Drosophila PGRP genes encode proteins that function as receptors mediating immune responses to bacteria. We show here that another member, PGRP-SC1B, has a totally different function because it has enzymatic activity and thereby can degrade peptidoglycan. A mass spectrometric analysis of the cleavage products demonstrates that the enzyme hydrolyzes the lactylamide bond between the glycan strand and the cross-linking peptides. This result assigns the protein as an N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28), and the corresponding gene is thus the first of this class to be described from a eukaryotic organism. Mutant forms of PGRP-SC1B lacking a potential zinc ligand are enzymatically inactive but retain their peptidoglycan affinity. The immunostimulatory properties of PGRP-SC1B-degraded peptidoglycan are much reduced. This is in striking contrast to lysozyme-digested peptidoglycan, which retains most of its elicitor activity. This points toward a scavenger function for PGRP-SC1B. Furthermore, a sequence homology comparison with phage T7 lysozyme, also an N-acetylmuramoyl-L-alanine amidase, shows that as many as six of the Drosophila PGRPs could belong to this class of proteins.

Peptidoglycan Recognition Proteins Involved in 1,3-β-D-Glucan-dependent Prophenoloxidase Activation System of Insect

“…Recently, it was reported that Drosophila PGRP-SC1B has a N-acetylmuramyl-L-alanine amidase activity and that it might have a scavenger function (47). Also, Drosophila PGRP-LB has been shown to have bacterial cell wall lytic activity (45).…”

Molecular and functional characterization of peptidoglycan-recognition protein SC2 (PGRP-SC2) from Nile tilapia (Oreochromis niloticus) involved in the immune response to Streptococcus agalactiae

“…[19,29] with minor modification. Briefly, 40 mg lysozyme-treated Staphylococcus aureus PGN (Sigma, USA) at a concentration of 1 mg/mL was incubated with 50 mg protein extract of rOn-PGRP-SC2 in Tris-ZnCl 2 buffer (20 mM TrisHCl, 150 mM NaCl, 10 mM ZnCl 2 , pH 7.2) or Tris buffer (20 mM TrisHCl, 150 mM NaCl, pH 7.2).…”

Molecular cloning and functional characterization of peptidoglycan recognition protein 6 in grass carp Ctenopharyngodon idella

“…The activation of insect PGRPs by Gram-positive or Gram-negative bacteria may trigger Toll (Gobert et al, 2003) and immune deficiency (Imd) signal transduction pathways (Takehana et al, 2002) and the prophenol-oxidase cascade (Takehana et al, 2002), which results in the production of antimicrobial effectors. In addition, some insect PGRPs such as Drosophila PGRP-SC1 and PGRP-LB are N-acetylmuramoyl-L-alanine amidases (Kim et al, 2003;Mellroth et al, 2003), which can hydrolyze proinflammatory peptidoglycans. One insect PGRP, Drosophila PGRP-SA, which is not an amidase, has an L,D-carboxypeptidase activity for diaminopimelic acid-type tetrapeptide peptidoglycan fragments (Chang et al, 2004).…”