HelicobacterCatalase Devoid of Catalytic Activity Protects the Bacterium against Oxidative Stress.
Catalase, a conserved and abundant enzyme found in all domains of life, dissipates the oxidant hydrogen peroxide (H2O2). The gastric pathogenHelicobacter pyloriundergoes host-mediated oxidant stress exposure, and its catalase contains oxidizable methionine (Met) residues. We hypothesized catalase may play a large stress-combating role independent of its classical catalytic one, namely quenching harmful oxidants through its recyclable Met residues, resulting in oxidant protection to the bacterium. TwoHelicobactermutant strains (katAH56AandkatAY339A) containing catalase without enzyme activity but that retain all Met residues were created. These strains were much more resistant to oxidants than a catalase-deletion mutant strain. The quenching ability of the altered versions was shown, whereby oxidant-stressed (HOCl-exposed)Helicobacterretained viability even upon extracellular addition of the inactive versions of catalase, in contrast to cells receiving HOCl alone. The importance of the methionine-mediated quenching to the pathogen residing in the oxidant-rich gastric mucus was studied. In contrast to a catalase-null strain, both site-change mutants proficiently colonized the murine gastric mucosa, suggesting that the amino acid composition-dependent oxidant-quenching role of catalase is more important than the well described H2O2-dissipating catalytic role. Over 100 years after the discovery of catalase, these findings reveal a new non-enzymatic protective mechanism of action for the ubiquitous enzyme.
From the Department of Microbiology, University of Georgia, Athens, Georgia 30602.
Stéphane L
SL
Benoit
From the Department of Microbiology, University of Georgia, Athens, Georgia 30602 rmaier@uga.edu.
Robert J
RJ
Maier
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D005753:Gastric Mucosa / Q000382:microbiology; D016998:Helicobacter / Q000187:drug effects / Q000201:enzymology*; D006997:Hypochlorous Acid / Q000494:pharmacology; D051379:Mice; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D017384:Sequence Deletion
D001426:Bacterial Proteins; D006997:Hypochlorous Acid; D002374:Catalase
antioxidant; bacterial metabolism; bacterial pathogenesis; infectious disease; microbiology; multifunctional enzyme; oxidative stress