title: Truncated hemoglobin HbN protects Mycobacterium bovis from nitric oxide.
abstract: Mycobacterium tuberculosis, the causative agent of human tuberculosis, and Mycobacterium bovis each express two genes, glbN and glbO, encoding distantly related truncated hemoglobins (trHbs), trHbN and trHbO, respectively. Here we report that disruption of M. bovis bacillus Calmette-Guérin glbN caused a dramatic reduction in the NO-consuming activity of stationary phase cells, and that activity could be restored fully by complementing knockout cells with glbN. Aerobic respiration of knockout cells was inhibited markedly by NO in comparison to that of wild-type cells, indicating a protective function for trHbN. TyrB10, which is highly conserved in trHbs and interacts with the bound oxygen, was found essential for NO consumption. Titration of oxygenated trHbN (trHbN.O(2)) with NO resulted in stoichiometric oxidation of the protein with nitrate as the major product of the reaction. The second-order rate constant for the reaction between trHbN.O(2) and NO at 23 degrees C was 745 microM(-1).s(-1), demonstrating that trHbN detoxifies NO 20-fold more rapidly than myoglobin. These results establish a role for a trHb and demonstrate an NO-metabolizing activity in M. tuberculosis or M. bovis. trHbN thus might play an important role in persistence of mycobacterial infection by virtue of trHbN's ability to detoxify NO.
authors.affiliation: Department of Biochemistry and Microbiology, Faculty of Sciences and Engineering, Laval University, QC, Canada.
authors.forename: Hugues
authors.initials: H
authors.lastname: Ouellet
authors.forename: Yannick
authors.initials: Y
authors.lastname: Ouellet
authors.forename: Christian
authors.initials: C
authors.lastname: Richard
authors.forename: Marie
authors.initials: M
authors.lastname: Labarre
authors.forename: Beatrice
authors.initials: B
authors.lastname: Wittenberg
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wittenberg
authors.forename: Michel
authors.initials: M
authors.lastname: Guertin
mesh_terms: D001426:Bacterial Proteins; D002455:Cell Division; D004305:Dose-Response Relationship, Drug; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009163:Mycobacterium bovis / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012119:Respiration; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D019076:Transgenes; D054793:Truncated Hemoglobins
chemical_list: D001426:Bacterial Proteins; C102539:GlbN protein, bacteria; D006454:Hemoglobins; D009566:Nitrates; D009573:Nitrites; D054793:Truncated Hemoglobins; D009569:Nitric Oxide; D012313:RNA; D010100:Oxygen