Functional characterization of a short peptidoglycan recognition protein from Chinese giant salamander (Andrias davidianus).

Shisi Ren,Qiaoqing Xu,Mingxian Chang,Qihuan Zhang,Zhitao Qi,Zisheng Wang,Guo Qiao,Jun Zou,Pin Nie

doi:10.18632/oncotarget.21470

Abstract

Peptidoglycan (PGN) recognition proteins (PGRPs) are important pattern recognition receptors (PRRs) involved in immune defense against bacterial infections. In this study, a short PGRP (termed AdPGRP-S1) was cloned and functionally characterized from Chinese giant salamander (Andrias davidianus), the largest extant urodela amphibian species. AdPGRP-S1 was 184 aa in length and shared 38.7%-54.9% sequence identities with other vertebrates’ short PGRPs. It contained one typical PGRP domain at the C-terminal region and several conserved amino acid (aa) residues involved in amidase and PGN binding. AdPGRP-S1 was constitutively expressed in all tissues examined, with the highest expression level seen in spleen and intestine. It has been shown that AdPGRP-S1 could bind and degrade Lys-PGN and Dap-PGN. Further, AdPGRP-S1 had antibacterial activity against the Gram-negative bacteria, Edwardsiella tarda, and was able to trigger the activation of NF-κB signaling. These results demonstrated that AdPGRP-S1 possesses multiple functions in pathogen recognition, mediating ceullular signaling, and initiating antibacterial response. This is the first functional study of a salamander PGRP, providing insight to further understand the functional evolution of verterbates’ PGRPs.

Highlights

Innate immunity is the first line of defense against invading microorganisms, and is triggered by recognition of pathogen associated molecular patterns (PAMPs) through host pattern recognition receptors (PRRs)
The open reading frame (ORF) of AdPGRP-S1 encoded 184 amino acids with a signal peptide of 17 aa predicted by the SignalP software
Several conserved residues important for the peptidoglycan recognition proteins (PGRPs) functions were identified in the PGRP domain, including four catalytic residues responsible for amidase activity (H49, Y84, H159 and C167), four residues involved in specific PGN recognition activity (K78, W79, R98 and V103), and ten possible substrate binding sites (H50, T51, C80, Y84, R98, A105, H106, N112, H159, T165, S166 and C167) (Figure 1)

Summary

Introduction

Innate immunity is the first line of defense against invading microorganisms, and is triggered by recognition of pathogen associated molecular patterns (PAMPs) through host pattern recognition receptors (PRRs). PAMPs are conserved molecular structures of microorganisms, including bacterial lipopolysaccharide (LPS) and peptidoglycan (PGN), fungal β-1,3-glucan and viral double-stranded RNA (dsRNA) [1]. Several families of PRRs have been identified in vertebrates, including tolllike receptors (TLRs), nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), retinoic acid inducible gene I-like receptors (RLRs), C-type lectin receptors (CLRs), and peptidoglycan recognition proteins (PGRPs) [2]. PGRPs were subsequently found to be conserved in the whole animal kingdom including insects [4], deuterostomes [5], fish [6] and mammals [7]. All PGRPs contain at least one C-terminal PGRP domain of 165 amino acids. PGRPs contain multi β-sheets and α-helices, which form an L-shaped groove involved in PGN binding [8]

Methods

Results

Conclusion