RESUMO
Mycobacterium tuberculosis is the causative agent of human tuberculosis, one of the most prevalent infectious diseases in the world. Its genome hosts the glbN and glbO genes coding for two proteins, truncated hemoglobin N (trHbN) and truncated hemoglobin O (trHbO), that belong to different groups (I and II, respectively) of the recently discovered trHb family of hemeproteins. The different expression pattern and kinetics rates constants for ligand association and NO oxidation rate suggest different functions for these proteins. Previous experimental and theoretical studies showed that, in trHbs, ligand migration along the internal tunnel cavity system is a key issue in determining the ligand-binding characteristics. The X-ray structure of trHbO has been solved and shows several internal cavities and secondary-docking sites. In this work, we present an extensive investigation of the tunnel/cavity system ofM. tuberculosis trHbO by means of computer-simulation techniques. We have computed the free-energy profiles for ligand migration along three found tunnels in the oxy and deoxy w.t. and mutant trHbO proteins. Our results show that multiple-ligand migration paths are possible and that several conserved residues such as TrpG8 play a key role in the ligand-migration regulation.
Assuntos
Proteínas de Bactérias/química , Proteínas Mutantes/química , Mycobacterium tuberculosis/metabolismo , Hemoglobinas Truncadas/química , Proteínas de Bactérias/genética , Cristalografia por Raios X , Ligantes , Proteínas Mutantes/genética , Mycobacterium tuberculosis/genética , Termodinâmica , Hemoglobinas Truncadas/genéticaAssuntos
Clonagem Molecular , Dados de Sequência Molecular , Hemoglobinas/genética , Hemoglobinas/metabolismo , Hemoglobinas/química , Homologia de Sequência de Aminoácidos , Ligantes , Modelos Moleculares , Mycobacterium leprae , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Proteínas de Bactérias/química , Sequência de Aminoácidos , Sequência de BasesRESUMO
Leprosy is an old, still dreaded infectious disease caused by the obligate intracellular bacterium Mycobacterium leprae. During the infectious process, M. leprae is faced with the host macrophagic environment, where the oxidative stress and NO release, combined with low pH, low pO2, and high pCO2, contribute to limit the growth of the bacilli. Comparative genomics has unraveled massive gene decay in M. leprae, linking the strictly parasitic lifestyle with the reductive genome evolution. Compared with Mycobacterium tuberculosis and Mycobacterium bovis, the leprosy bacillus has lost most of the genes involved in the detoxification of reactive oxygen and nitrogen species. The very low reactivity of the unique truncated hemoglobin retained by M. leprae could account for the susceptibility of this exceptionally slow-growing microbe to NO.