title: Streptococcus mutans H2O2-forming NADH oxidase is an alkyl hydroperoxide reductase protein.
abstract: Nox-1 from Streptococcus mutans, the bacteria which cause dental caries, was previously identified as an H2O2-forming reduced nicotinamide adenine dinucleotide (NADH) oxidase. Nox-1 is homologous with the flavoprotein component, AhpF, of Salmonella typhimurium alkyl hydroperoxide reductase. A partial open reading frame upstream of nox1, homologous with the other (peroxidase) component, ahpC, from the S. typhimurium system, was also identified. We report here the complete sequence of S. mutans ahpC. Analyses of purified AhpC together with Nox-1 have verified that these proteins act as a cysteine-based peroxidase system in S. mutans, catalyzing the NADH-dependent reduction of organic hydroperoxides or H2O2 to their respective alcohols and/or H2O. These proteins also catalyze the four-electron reduction of O2 to H2O2, clarifying the role of Nox-1 as a protective protein against oxygen toxicity. Major differences between Nox-1 and AhpF include: (i) the absolute specificity of Nox-1 for NADH; (ii) lower amounts of flavin semiquinone and a more prominent FADH2 to NAD+ charge transfer absorbance band stabilized by Nox-1; and (iii) even higher redox potentials of disulfide centers relative to flavin for Nox-1. Although Nox-1 and AhpC from S. mutans were shown to play a protective role against oxidative stress in vitro and in vivo in Escherichia coli, the lack of a significant effect on deletion of these genes from S. mutans suggests the presence of additional antioxidant proteins in these bacteria.
authors.affiliation: Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem 27157, NC, USA. lbpoole@wfubmc.edu
authors.forename: L B
authors.initials: LB
authors.lastname: Poole
authors.forename: M
authors.initials: M
authors.lastname: Higuchi
authors.forename: M
authors.initials: M
authors.lastname: Shimada
authors.forename: M L
authors.initials: ML
authors.lastname: Calzi
authors.forename: Y
authors.initials: Y
authors.lastname: Kamio
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006090:Gram-Negative Bacteria / Q000201:enzymology; D006094:Gram-Positive Bacteria / Q000201:enzymology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000074624:NADPH Oxidase 1; D010544:Peroxidases / Q000235:genetics / Q000378:metabolism; D054464:Peroxiredoxins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013295:Streptococcus mutans / Q000201:enzymology* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D006861:Hydrogen Peroxide; D010544:Peroxidases; D054464:Peroxiredoxins; C515937:ahpC protein, E coli; D009247:NADH, NADPH Oxidoreductases; D000074624:NADPH Oxidase 1; C515938:ahpF protein, E coli