AsnB Mediates Amidation of Meso-Diaminopimelic Acid Residues in the Peptidoglycan of Listeria monocytogenes and Affects Bacterial Surface Properties and Host Cell Invasion

Lei Sun; Gil Rogiers; Pascal Courtin; Marie-Pierre Chapot-Chartier; Hélène Bierne; Chris W Michiels

doi:10.3389/fmicb.2021.760253

AsnB Mediates Amidation of Meso-Diaminopimelic Acid Residues in the Peptidoglycan of Listeria monocytogenes and Affects Bacterial Surface Properties and Host Cell Invasion

Front Microbiol. 2021 Oct 15:12:760253. doi: 10.3389/fmicb.2021.760253. eCollection 2021.

Authors

Lei Sun¹, Gil Rogiers¹, Pascal Courtin², Marie-Pierre Chapot-Chartier², Hélène Bierne², Chris W Michiels¹

Affiliations

¹ Laboratory of Food Microbiology, Department of Microbial and Molecular Systems (M2S) and Leuven Food Science and Nutrition Research Center (LFoRCe), KU Leuven, Leuven, Belgium.
² INRAE, AgroParisTech, Micalis Institute, Université Paris-Saclay, Jouy-en-Josas, France.

Abstract

A mutant of Listeria monocytogenes ScottA with a transposon in the 5' untranslated region of the asnB gene was identified to be hypersensitive to the antimicrobial t-cinnamaldehyde. Here, we report the functional characterization of AsnB in peptidoglycan (PG) modification and intracellular infection. While AsnB of Listeria is annotated as a glutamine-dependent asparagine synthase, sequence alignment showed that this protein is closely related to a subset of homologs that catalyze the amidation of meso-diaminopimelic acid (mDAP) residues in the peptidoglycan of other bacterial species. Structural analysis of peptidoglycan from an asnB mutant, compared to that of isogenic wild-type (WT) and complemented mutant strains, confirmed that AsnB mediates mDAP amidation in L. monocytogenes. Deficiency in mDAP amidation caused several peptidoglycan- and cell surface-related phenotypes in the asnB mutant, including formation of shorter but thicker cells, susceptibility to lysozyme, loss of flagellation and motility, and a strong reduction in biofilm formation. In addition, the mutant showed reduced invasion of human epithelial JEG-3 and Caco-2 cells. Analysis by immunofluorescence microscopy revealed that asnB inactivation abrogated the proper display at the listerial surface of the invasion protein InlA, which normally gets cross-linked to mDAP via its LPXTG motif. Together, this work shows that AsnB of L. monocytogenes, like several of its homologs in related Gram-positive bacteria, mediates the amidation of mDAP residues in the peptidoglycan and, in this way, affects several cell wall and cell surface-related properties. It also for the first time implicates the amidation of peptidoglycan mDAP residues in cell wall anchoring of InlA and in bacterial virulence.

Keywords: Listeria monocytogenes; biofilm formation; host cell invasion; lysozyme sensitivity; meso-diaminopimelic acid; motility; peptidoglycan modification; virulence.