Peptidoglycan and Nod Receptor

Immunity, 2007

Science, 2003

Although the role of Toll-like receptors in extracellular bacterial sensing has been investigated intensively, intracellular detection of bacteria through Nod molecules remains largely uncharacterized. Here, we show that human Nod1 specifically detects a unique diaminopimelate-containing N -acetylglucosamine– N -acetylmuramic acid (GlcNAc-MurNAc) tripeptide motif found in Gram-negative bacterial peptidoglycan, resulting in activation of the transcription factor NF-κB pathway. Moreover, we show that in epithelial cells (which represent the first line of defense against invasive pathogens), Nod1is indispensable for intracellular Gram-negative bacterial sensing.

Journal of Biological Chemistry, 2007

Nod1 is an intracellular protein that is involved in recognition of bacterial molecules and whose genetic variation has been linked to several inflammatory diseases. Previous studies suggested that the recognition core of Nod1stimulatory molecules is γ-D-glutamyl-mesodiaminopimelic acid (iE-DAP), but the identity of the major Nod1-stimulatory molecule produced by bacteria remains unknown. Here we show that bacteria produce lipophilic molecules capable of stimulating Nod1. Analysis of synthetic compounds revealed stereoselectivity of the DAP residue and that conjugation of lipophilic acyl residues specifically enhances the Nod1-stimulatory activity of the core iE-DAP. Furthermore, we demonstrate that lipophilic molecules induce and/or enhance the secretion of innate immune mediators from primary mouse mesothelial cells and human monocytic MonoMac6 cells and this effect is mediated through Nod1. These results provide insight into the mechanism of immune recognition via Nod1 which might be useful in design and testing of novel immunoregulators. The innate immune receptors recognize specific molecules that are commonly found in microbes and induce host defense responses to eliminate invading pathogens (1). These pathogen-recognizing receptors (PRRs) include membrane-bound Toll-like receptors (TLRs) as well as cytosolic Nod-like receptors (NLRs) and RIG-I family proteins. These three classes of

Journal of Biological Chemistry, 2005

Microbial Drug Resistance, 2012

Peptidoglycan recognition proteins (PGRPs) are conserved from insects to mammals and function in antibacterial immunity. We have revealed a novel mechanism of bacterial killing by innate immune system, in which mammalian PGRPs bind to bacterial cell wall or outer membrane and exploit bacterial stress defense response to kill bacteria. PGRPs enter Gram-positive cell wall at the site of daughter cell separation during cell division. In Bacillus subtilis PGRPs activate the CssR-CssS two-component system that detects and disposes of misfolded proteins exported out of bacterial cells. This activation results in membrane depolarization, production of hydroxyl radicals, and cessation of intracellular peptidoglycan, protein, RNA, and DNA synthesis, which are responsible for bacterial death. PGRPs also bind to the outer membrane in Escherichia coli and activate functionally homologous CpxA-CpxR two-component system, which also results in bacterial death. We excluded other potential bactericidal mechanisms, such as inhibition of extracellular peptidoglycan synthesis, hydrolysis of peptidoglycan, and membrane permeabilization. In vivo, mammalian PGRPs are expressed in polymorphonuclear leukocytes, skin, salivary glands, oral cavity, intestinal tract, eyes, and liver. They control acquisition and maintenance of beneficial normal gut microflora, which protects the host from enhanced inflammation, tissue damage, and colitis. Discovery and Functions of PGRPs P eptidoglycan recognition proteins (PGRPs or PGLYRPs) were discovered in 1996 in the silkworm, Bombyx mori, as the sensors of bacterial peptidoglycan that activate prophenoloxidase cascade. 44 This cascade is a part of innate immune response in invertebrates and generates quinones, which are toxic to microorganisms, and melanin pigments, which restrict spreading of the microorganisms within the host. The first PGRP was cloned in a moth Trichoplusia ni, which led to the discovery of highly conserved human and mouse orthologs. 19 Sequencing of the fruit fly, mosquito, and human genomes led to the discovery of diversified families of PGRPs, conserved from insects to mammals. 3,29,41 PGRPs function in antibacterial defenses and innate immunity. Insects have many PGRPs with diverse functions. Insect PGRPs sense bacteria and trigger host defense pathways, which generate antibacterial products, defend against infections, and regulate insects' microbiomes. Some insect PGRPs hydrolyze or nonenzymatically neutralize proinflammatory bacterial peptidoglycan and thus limit inflammation. 9,33,34 Mammals have four PGRP genes, Pglyrp1, Pglyrp2, Pglyrp3, and Pglyrp4, which were initially named PGRP-S, PGRP-L, PGRP-Ia, and PGRP-Ib (for ''short,'' ''long,'' or ''intermediate'' transcripts, respectively), by analogy to insect PGRPs. 29 PGLYRP1, PGLYRP3, and PGLYRP4 are directly bactericidal for both Gram-positive and Gram-negative bacteria, 11,28,30,37,39 and PGLYRP2 is a peptidoglycan-lytic amidase 14,40,45 and also has bactericidal activity. PGLYRP1 is mainly present in PMN's granules, PGLYRP2 is made in the liver and secreted into blood and is also induced in epithelial cells, and PGLYRP3 and PGLYRP4 are produced on the skin and mucous membranes, and in sweat, sebum, and saliva. 11,26,28-30,35-40,45 This review will first focus on the question how PGRPs kill bacteria, and then will briefly discuss the in vivo consequences of antibacterial activity of PGRPs-their effect on microbiome and inflammation. How do PGRPs Kill Bacteria?-The Initial Hypotheses Our first hypothesis was that PGRPs kill bacteria by inhibiting the transglycosylation or transpeptidation steps in peptidoglycan synthesis 10,30,39 because (a) PGRPs bind to the

Gut, 2011

Background and aims Inflammatory bowel disease (IBD) has been linked to a loss of tolerance towards the resident microflora. Therapeutic use of probiotics is known to be strain specific, but precise mechanisms remain unclear. The role of NOD2 signalling and the protective effect of Lactobacillus peptidoglycan (PGN) and derived muropeptides in experimental colitis were evaluated. Methods The anti-inflammatory capacity of lactobacilli and derived bacterial compounds was evaluated using the 2,4,6-trinitrobenzene sulfonic acid (TNBS) colitis model. The role of NOD2, MyD88 and interleukin 10 (IL-10) in this protection was studied using Nod2 À/À , MyD88 À/À and Il10-deficient mice, while induction of regulatory dendritic cells (DCs) was monitored through the expansion of CD103 + DCs in mesenteric lymph nodes or after adoptive transfer of bone marrow-derived DCs. The development of regulatory T cells was investigated by following the expansion of CD4 + FoxP3 + cells. High-performance liquid chromatography and mass spectrometry were used to analyse the PGN structural differences.

Biochemical Journal, 2016

Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) is an intracellular pattern recognition receptor that recognizes bacterial peptidoglycan (PG) containing mesodiaminopimelic acid (mesoDAP) and activates the innate immune system. Interestingly, a few pathogenic and commensal bacteria modify their PG stem peptide by amidation of mesoDAP (mesoDAP NH2 ). In the present study, NOD1 stimulation assays were performed using bacterial PG containing mesoDAP (PG DAP ) and mesoDAP NH2 (PG DAPNH2 ) to understand the differences in their biomolecular recognition mechanism. PG DAP was effectively recognized, whereas PG DAPNH2 showed reduced recognition by the NOD1 receptor. Restimulation of the NOD1 receptor, which was initially stimulated with PG DAP using PG DAPNH2 , did not show any further NOD1 activation levels than with PG DAP alone. But the NOD1 receptor initially stimulated with PG DAPNH2 responded effectively to restimulation with PG DAP . The biomolecular structure-recognition relationship of the ligand-sensing leucine-rich repeat (LRR) domain of human NOD1 (NOD1-LRR) with PG DAP and PG DAPNH2 was studied by different computational techniques to further understand the molecular basis of our experimental observations. The D-Glu-mesoDAP motif of GMTP DAP , which is the minimum essential motif for NOD1 activation, was found involved in specific interactions at the recognition site, but the interactions of the corresponding D-Glu-mesoDAP motif of PG DAPNH2 occur away from the recognition site of the NOD1 receptor. Hot-spot residues identified for effective PG recognition by NOD1-LRR include W820, G821, D826 and N850, which are evolutionarily conserved across different host species. These integrated results thus successfully provided the atomic level and biochemical insights on how PGs containing mesoDAP NH2 evade NOD1-LRR receptor recognition.

Nature Immunology, 2004

Epithelial cells can respond to conserved bacterial products that are internalized after either bacterial invasion or liposome treatment of cells. We report here that the noninvasive Gram-negative pathogen Helicobacter pylori was recognized by epithelial cells via Nod1, an intracellular pathogen-recognition molecule with specificity for Gram-negative peptidoglycan. Nod1 detection of H. pylori depended on the delivery of peptidoglycan to host cells by a bacterial type IV secretion system, encoded by the H. pylori cag pathogenicity island. Consistent with involvement of Nod1 in host defense, Nod1-deficient mice were more susceptible to infection by cag pathogenicity island-positive H. pylori than were wild-type mice. We propose that sensing of H. pylori by Nod1 represents a model for host recognition of noninvasive pathogens.

Journal of Biological Chemistry, 1996

Cell Host & Microbe, 2010