Enterococcus faecium secreted antigen A generates muropeptides to enhance host immunity and limit bacterial pathogenesis.

Byungchul Kim,Yen-Chih Wang,Howard C Hang,Jeanne Salje,Jin Young Kang,Charles W Hespen,Deena A Oren,Kavita J Rangan,Juliel Espinosa,Virginia A Pedicord

doi:10.7554/elife.45343

Abstract

We discovered that Enterococcus faecium (E. faecium), a ubiquitous commensal bacterium, and its secreted peptidoglycan hydrolase (SagA) were sufficient to enhance intestinal barrier function and pathogen tolerance, but the precise biochemical mechanism was unknown. Here we show E. faecium has unique peptidoglycan composition and remodeling activity through SagA, which generates smaller muropeptides that more effectively activates nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in mammalian cells. Our structural and biochemical studies show that SagA is a NlpC/p60-endopeptidase that preferentially hydrolyzes crosslinked Lys-type peptidoglycan fragments. SagA secretion and NlpC/p60-endopeptidase activity was required for enhancing probiotic bacteria activity against Clostridium difficile pathogenesis in vivo. Our results demonstrate that the peptidoglycan composition and hydrolase activity of specific microbiota species can activate host immune pathways and enhance tolerance to pathogens.

Highlights

The microbiota provides an important barrier to enteric infections and encodes microbe-associated molecular patterns as well as secondary metabolites, which can prime host immunity or attenuate pathogen fitness (Buffie and Pamer, 2013; Milshteyn et al, 2018)
Typhimurium was abrogated in Nod2-/- mice in vivo and secreted antigen A (SagA) contains predicted peptidoglycan hydrolase (Pedicord et al, 2016), we focused on whether E. faecium and SagA exhibit unique peptidoglycan composition and activity
Deletion or loss-of-function mutations of nucleotide-binding oligomerization domain-containing protein 2 (NOD2) in particular are associated with gut microbiota dysbiosis, invasion of pathobionts and inflammatory bowel disease (IBD) (Caruso et al, 2014; Philpott et al, 2014), which suggests that NOD2 is important for sensing peptidoglycan in the gut and priming innate immune pathways to maintain intestinal barrier function and preventing microbiota- and pathogen-induced inflammation (Al Nabhani et al, 2017; Caruso et al, 2014; Philpott et al, 2014)

Summary

Introduction

The microbiota provides an important barrier to enteric infections and encodes microbe-associated molecular patterns as well as secondary metabolites, which can prime host immunity or attenuate pathogen fitness (Buffie and Pamer, 2013; Milshteyn et al, 2018). Butyrate production by Clostridial strains (clusters XIVa and IV) can attenuate inflammation by inducing peripheral regulatory T cells (Arpaia et al, 2013; Furusawa et al, 2013; Smith et al, 2013) and suppress reactive metabolites to prevent the expansion of enteric pathogens (Byndloss et al, 2017). Commensal bacteria such as Clostridium scindens can generate secondary bile acids that mediate colonization resistance toward pathogens such as Clostridium difficile (Buffie et al, 2015).

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