Affiliation:
1. Department of Medical Microbiology and Immunology, University of Wisconsin—Madison, Madison, Wisconsin, USA
Abstract
ABSTRACT
Neisseria gonorrhoeae
gonococcus (GC) is a Gram-negative betaproteobacterium and causative agent of the sexually transmitted infection gonorrhea. During growth, GC releases lipooligosaccharide (LOS) and peptidoglycan (PG) fragments, which contribute significantly to the inflammatory damage observed during human infection. In ascending infection of human Fallopian tubes, inflammation leads to increased risk of ectopic pregnancy, pelvic inflammatory disease, and sterility. Of the PG fragments released by GC, most are disaccharide peptide monomers, and of those, 80% have tripeptide stems despite the observation that tetrapeptide stems make up 80% of the assembled cell wall. We identified a serine-protease
l
,
d
-carboxypeptidase, NGO1274 (LdcA), as the enzyme responsible for converting cell wall tetrapeptide-stem PG to released tripeptide-stem PG. Unlike characterized cytoplasmic LdcA homologs in gammaproteobacteria, LdcA in GC is exported to the periplasm, and its localization is critical for its activity in modifying PG fragments for release. Distinct among other characterized
l
,
d
-carboxypeptidases, LdcA from GC is also capable of catalyzing the cleavage of specific peptide cross-bridges (endopeptidase activity). To define the role of
ldcA
in pathogenesis, we demonstrate that
ldcA
disruption results in both loss of NOD1-dependent NF-κB activation and decreased NOD2-dependent NF-κB activation while not affecting Toll-like receptor (TLR) agonist release. Since the human intracellular peptidoglycan receptor NOD1 (hNOD1) specifically recognizes PG fragments with a terminal
meso
-DAP rather than
d
-alanine, we conclude that LdcA is required for GC to provoke NOD1-dependent responses in cells of the human host.
IMPORTANCE
The macromolecular meshwork of peptidoglycan serves essential functions in determining bacterial cell shape, protecting against osmotic lysis, and defending cells from external assaults. The conserved peptidoglycan structure, however, is also recognized by eukaryotic pattern recognition receptors, which can trigger immune responses against bacteria. Many bacteria can induce an inflammatory response through the intracellular peptidoglycan receptor NOD1, but
Neisseria gonorrhoeae
serves as an extreme example, releasing fragments of peptidoglycan into the environment during growth that specifically antagonize human NOD1. Understanding the peptidoglycan breakdown mechanisms that allow
Neisseria
to promote NOD1 activation, rather than avoiding or suppressing immune detection, is critical to understanding the pathogenesis of this increasingly drug-resistant organism. We identify a peptidoglycan
l
,
d
-carboxypeptidase responsible for converting liberated peptidoglycan fragments into the human NOD1 agonist and find that the same enzyme has endopeptidase activity on certain peptidoglycan cross-links, the first described combination of those two activities in a single enzyme.
Funder
HHS | NIH | National Institute of Allergy and Infectious Diseases
Publisher
American Society for Microbiology
Cited by
32 articles.
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