A new family of lysozyme inhibitors contributing to lysozyme tolerance in gram-negative bacteria.
Lysozymes are ancient and important components of the innate immune system of animals that hydrolyze peptidoglycan, the major bacterial cell wall polymer. Bacteria engaging in commensal or pathogenic interactions with an animal host have evolved various strategies to evade this bactericidal enzyme, one recently proposed strategy being the production of lysozyme inhibitors. We here report the discovery of a novel family of bacterial lysozyme inhibitors with widespread homologs in gram-negative bacteria. First, a lysozyme inhibitor was isolated by affinity chromatography from a periplasmic extract of Salmonella Enteritidis, identified by mass spectrometry and correspondingly designated as PliC (periplasmic lysozyme inhibitor of c-type lysozyme). A pliC knock-out mutant no longer produced lysozyme inhibitory activity and showed increased lysozyme sensitivity in the presence of the outer membrane permeabilizing protein lactoferrin. PliC lacks similarity with the previously described Escherichia coli lysozyme inhibitor Ivy, but is related to a group of proteins with a common conserved COG3895 domain, some of them predicted to be lipoproteins. No function has yet been assigned to these proteins, although they are widely spread among the Proteobacteria. We demonstrate that at least two representatives of this group, MliC (membrane bound lysozyme inhibitor of c-type lysozyme) of E. coli and Pseudomonas aeruginosa, also possess lysozyme inhibitory activity and confer increased lysozyme tolerance upon expression in E. coli. Interestingly, mliC of Salmonella Typhi was picked up earlier in a screen for genes induced during residence in macrophages, and knockout of mliC was shown to reduce macrophage survival of S. Typhi. Based on these observations, we suggest that the COG3895 domain is a common feature of a novel and widespread family of bacterial lysozyme inhibitors in gram-negative bacteria that may function as colonization or virulence factors in bacteria interacting with an animal host.
Callewaert
Lien
L
Laboratory of Food Microbiology, Department of Microbial and Molecular Systems (M2S), Katholieke Universiteit Leuven, Leuven, Belgium.
Aertsen
Abram
A
Deckers
Daphne
D
Vanoirbeek
Kristof G A
KG
Vanderkelen
Lise
L
Van Herreweghe
Joris M
JM
Masschalck
Barbara
B
Nakimbugwe
Dorothy
D
Robben
Johan
J
Michiels
Chris W
CW
D000818:Animals; D000890:Anti-Infective Agents / Q000037:antagonists & inhibitors / Q000276:immunology*; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D002645:Chickens; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000276:immunology*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D020868:Gene Silencing; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance; D009113:Muramidase / Q000037:antagonists & inhibitors / Q000276:immunology*; D033902:Periplasmic Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D011550:Pseudomonas aeruginosa / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D012477:Salmonella enteritidis / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D037521:Virulence Factors
D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D033902:Periplasmic Binding Proteins; D037521:Virulence Factors; C421864:hen egg lysozyme; D009113:Muramidase