Neisseria gonorrhoeae Lytic Transglycosylases LtgA and LtgD Reduce Host Innate Immune Signaling through TLR2 and NOD2

Abstract

Neisseria gonorrhoeae releases anhydro peptidoglycan monomers during growth through the action of two lytic transglycosylases encoded in the N. gonorrhoeae genome, LtgA and LtgD. Because peptidoglycan and peptidoglycan components activate innate immune signaling, we hypothesized that the activity of LtgA and LtgD would influence the host responses to gonococcal infection. N. gonorrhoeae lacking LtgA and LtgD caused increased host production of inflammatory cytokines IL-1β and TNF-α. Culture supernatants from ΔltgA/ΔltgD N. gonorrhoeae contain more shed outer membrane-associated proteins and multimeric peptidoglycan fragments rather than monomers. These culture supernatants were more potent activators of host TLR2 and NOD2 signaling when compared to supernatants from the isogenic parental N. gonorrhoeae strain. Purified peptidoglycan monomers containing anhydro muramic acid produced by LtgA were poor stimulators of NOD2 while peptidoglycan monomers containing reducing muramic acid produced by host lysozyme were potent stimulators of NOD2. These data indicate that LtgA and LtgD reduce recognition of N. gonorrhoeae by TLR2 and NOD2.

The lytic transglycosylase MltB connects membrane homeostasis and in vivo fitness of Acinetobacter baumannii

“…The contribution of LTs to pathogenesis was recently observed in N. gonorrhoeae, B. abortus and E. tarda (Liu et al, 2012;Bao et al, 2017;Knilans et al, 2017;Ragland et al, 2017). However, the molecular mechanisms connecting LTs to pathogenesis are not well defined, especially in A. baumannii.…”

“…These enzymes are involved in remodeling of the PG layer and releasing PG fragments (1,6-anhydro-muropeptides), and consequently, important for cell wall integrity (Dik et al, 2017). Recently, it was shown that LTs are important for pathogenesis in Neisseria gonorrhoeae, Brucella abortus and Edwardsiella tarda (Bao et al, 2017;Knilans et al, 2017;Liu et al, 2012;Ragland et al, 2017).…”

Attention Seeker: Production, Modification, and Release of Inflammatory Peptidoglycan Fragments in Neisseria Species

“…Human NOD1 senses free tripeptide and tripeptide monomer and is expressed by many different cell types in humans (33)(34)(35). Human NOD2 binds to muramyl dipeptide (MurNAc L-alanine-D-glutamate) and PG monomers with a reducing end and is expressed by a limited set of cell types, including leukocytes and epithelial cells (36)(37)(38)(39)(40). Curiously, murine NOD1 recognizes tetrapeptide monomer instead of tripeptide monomer (41).…”

Neisseria gonorrhoeae PBP3 and PBP4 Facilitate NOD1 Agonist Peptidoglycan Fragment Release and Survival in Stationary Phase

“…Among the PG fragments released by N. gonorrhoeae, the NOD1 agonists are the disaccharide tripeptide monomer (GlcNAc-anhydroMurNAc-L-Ala-D-Glu-meso-DAP) and the free tripeptide (L-Ala-D-Glu-meso-DAP) (11,19). NOD2 recognizes whole sacculi, PG containing MurNAc and terminating with the dipeptide (MurNAc-L-Ala-D-Glu), and monomeric PG fragments that have a free hydroxyl at the reducing end (20)(21)(22). For N. gonorrhoeae, the NOD2 agonists include large PG fragments generated by autolysis and disaccharide-dipeptide monomers (GlcNAc-anhMurNAc-L-Ala-D-Glu).…”

“…For N. gonorrhoeae, the NOD2 agonists include large PG fragments generated by autolysis and disaccharide-dipeptide monomers (GlcNAc-anhMurNAc-L-Ala-D-Glu). A third NOD2 agonist is generated by host lysozyme acting on glycosidically linked PG dimers and thereby creating PG monomers with a reducing end (22). Previous studies have demonstrated the roles of lytic transglycosylases LtgA and LtgD in producing toxic, monomeric PG fragments, including the disaccharide tripeptide monomer (8).…”